[PATCH] KVM: arm64: Disable LTO in hyp

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):
  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

As LTO is not really necessary for the hypervisor code, disable it for
the hyp directory to fix the build.

Link: https://github.com/ClangBuiltLinux/linux/issues/1317
Reported-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/kvm/hyp/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 687598e41b21..e8116016e6a8 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile

@@ -11,3 +11,6 @@ subdir-ccflags-y := -I$(incdir)				\
 		    $(DISABLE_STACKLEAK_PLUGIN)
 
 obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
+
+# Disable LTO for the files in this directory
+KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))

base-commit: f69d02e37a85645aa90d18cacfff36dba370f797
-- 
2.30.1.766.gb4fecdf3b7-goog


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On Thu, 04 Mar 2021 18:45:44 +0000,
Sami Tolvanen [off-list ref] wrote:

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):

I assume this message is only an oddity, right? Because
__guest_enter() is as far as you can imagine from irqbypass.c...

  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

As LTO is not really necessary for the hypervisor code, disable it for
the hyp directory to fix the build.

Can you shed some light on what the problem is exactly?

Can this be reduced to the nvhe part of the tree? The rest of the
hypervisor should support being built with LTO, I'd expect. Or am I
missing something more significant?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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On Thu, Mar 4, 2021 at 11:15 AM Marc Zyngier [off-list ref] wrote:

On Thu, 04 Mar 2021 18:45:44 +0000,
Sami Tolvanen [off-list ref] wrote:

quoted

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):

I assume this message is only an oddity, right? Because
__guest_enter() is as far as you can imagine from irqbypass.c...

I'm not sure what's up with the filename in the error message. Fangrui
or Nick probably have a better idea.

quoted

  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

As LTO is not really necessary for the hypervisor code, disable it for
the hyp directory to fix the build.

Can you shed some light on what the problem is exactly?

I assume hyp_panic() ends up being placed too far from __guest_enter()
when the kernel is large enough. Possibly something to do with LLVM
always splitting functions into separate sections with LTO. I'm not
sure why the linker cannot shuffle things around to make everyone
happy in this case, but I confirmed that this patch also fixes the
build issue for me:

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index af8e940d0f03..128197b7c794 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c

@@ -214,7 +214,7 @@ static void __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 }
 NOKPROBE_SYMBOL(__hyp_call_panic);

-void __noreturn hyp_panic(void)
+void __noreturn hyp_panic(void) __section(".text")
 {
        u64 spsr = read_sysreg_el2(SYS_SPSR);
        u64 elr = read_sysreg_el2(SYS_ELR);

quoted

Link: https://github.com/ClangBuiltLinux/linux/issues/1317
Reported-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/kvm/hyp/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 687598e41b21..e8116016e6a8 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile

@@ -11,3 +11,6 @@ subdir-ccflags-y := -I$(incdir)                             \
                  $(DISABLE_STACKLEAK_PLUGIN)

 obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
+
+# Disable LTO for the files in this directory
+KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))

base-commit: f69d02e37a85645aa90d18cacfff36dba370f797

Can this be reduced to the nvhe part of the tree? The rest of the
hypervisor should support being built with LTO, I'd expect. Or am I
missing something more significant?

No, this error appears to be about hyp_panic() in the vhe code. While
I'm not sure how beneficial LTO is in hypervisor code, there shouldn't
be any other reason we can't use it there.

Sami

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On Thu, 04 Mar 2021 21:25:41 +0000,
Sami Tolvanen [off-list ref] wrote:

We're getting into black-magic territory here. Why wouldn't hyp_panic
be in the .text section already?

quoted

quoted

Link: https://github.com/ClangBuiltLinux/linux/issues/1317
Reported-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/kvm/hyp/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 687598e41b21..e8116016e6a8 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile

@@ -11,3 +11,6 @@ subdir-ccflags-y := -I$(incdir)                             \
                  $(DISABLE_STACKLEAK_PLUGIN)

 obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
+
+# Disable LTO for the files in this directory
+KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS))

base-commit: f69d02e37a85645aa90d18cacfff36dba370f797

Can this be reduced to the nvhe part of the tree? The rest of the
hypervisor should support being built with LTO, I'd expect. Or am I
missing something more significant?

No, this error appears to be about hyp_panic() in the vhe code. While
I'm not sure how beneficial LTO is in hypervisor code, there shouldn't
be any other reason we can't use it there.

The VHE part of the hypervisor is the kernel itself, and not any
different from the rest of the code. It should be able to benefit from
LTO. On the contrary, the nVHE part is what could do without LTO,
given that it is essentially a separate object that happens to be
bundled with the kernel.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

_______________________________________________
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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

On Thu, Mar 4, 2021 at 2:17 PM Marc Zyngier [off-list ref] wrote:

On Thu, 04 Mar 2021 21:25:41 +0000,
Sami Tolvanen [off-list ref] wrote:

quoted

On Thu, Mar 4, 2021 at 11:15 AM Marc Zyngier [off-list ref] wrote:

quoted

On Thu, 04 Mar 2021 18:45:44 +0000,
Sami Tolvanen [off-list ref] wrote:

quoted

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):

I assume this message is only an oddity, right? Because
__guest_enter() is as far as you can imagine from irqbypass.c...

I'm not sure what's up with the filename in the error message. Fangrui
or Nick probably have a better idea.

quoted

quoted

  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

As LTO is not really necessary for the hypervisor code, disable it for
the hyp directory to fix the build.

Can you shed some light on what the problem is exactly?

I assume hyp_panic() ends up being placed too far from __guest_enter()
when the kernel is large enough. Possibly something to do with LLVM
always splitting functions into separate sections with LTO. I'm not
sure why the linker cannot shuffle things around to make everyone
happy in this case, but I confirmed that this patch also fixes the
build issue for me:

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index af8e940d0f03..128197b7c794 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c

@@ -214,7 +214,7 @@ static void __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 }
 NOKPROBE_SYMBOL(__hyp_call_panic);

-void __noreturn hyp_panic(void)
+void __noreturn hyp_panic(void) __section(".text")
 {
        u64 spsr = read_sysreg_el2(SYS_SPSR);
        u64 elr = read_sysreg_el2(SYS_ELR);

We're getting into black-magic territory here. Why wouldn't hyp_panic
be in the .text section already?

It's not quite black magic. LLVM essentially flips on
-ffunction-sections with LTO and therefore, hyp_panic() will be in
.text.hyp_panic in vmlinux.o, while __guest_enter() will be in .text.
Everything ends up in .text when we link vmlinux, of course.

$ readelf --sections vmlinux.o | grep hyp_panic
  [3936] .text.hyp_panic   PROGBITS         0000000000000000  004b56e4

Sami

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On Thu, Mar 4, 2021 at 2:34 PM Sami Tolvanen [off-list ref] wrote:

On Thu, Mar 4, 2021 at 2:17 PM Marc Zyngier [off-list ref] wrote:

quoted

On Thu, 04 Mar 2021 21:25:41 +0000,
Sami Tolvanen [off-list ref] wrote:

quoted

On Thu, Mar 4, 2021 at 11:15 AM Marc Zyngier [off-list ref] wrote:

quoted

On Thu, 04 Mar 2021 18:45:44 +0000,
Sami Tolvanen [off-list ref] wrote:

quoted

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):

I assume this message is only an oddity, right? Because
__guest_enter() is as far as you can imagine from irqbypass.c...

I'm not sure what's up with the filename in the error message. Fangrui
or Nick probably have a better idea.

quoted

quoted

  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

As LTO is not really necessary for the hypervisor code, disable it for
the hyp directory to fix the build.

Can you shed some light on what the problem is exactly?

I assume hyp_panic() ends up being placed too far from __guest_enter()
when the kernel is large enough. Possibly something to do with LLVM
always splitting functions into separate sections with LTO. I'm not
sure why the linker cannot shuffle things around to make everyone
happy in this case, but I confirmed that this patch also fixes the
build issue for me:

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index af8e940d0f03..128197b7c794 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c

@@ -214,7 +214,7 @@ static void __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 }
 NOKPROBE_SYMBOL(__hyp_call_panic);

-void __noreturn hyp_panic(void)
+void __noreturn hyp_panic(void) __section(".text")
 {
        u64 spsr = read_sysreg_el2(SYS_SPSR);
        u64 elr = read_sysreg_el2(SYS_ELR);

We're getting into black-magic territory here. Why wouldn't hyp_panic
be in the .text section already?

It's not quite black magic. LLVM essentially flips on
-ffunction-sections with LTO and therefore, hyp_panic() will be in
.text.hyp_panic in vmlinux.o, while __guest_enter() will be in .text.
Everything ends up in .text when we link vmlinux, of course.

$ readelf --sections vmlinux.o | grep hyp_panic
  [3936] .text.hyp_panic   PROGBITS         0000000000000000  004b56e4

Note that disabling LTO here has essentially the same effect as using
__section(".text"). It stops the compiler from splitting these
functions into .text.* sections and makes it less likely that
hyp_panic() ends up too far away from __guest_enter().

If neither of these workarounds sound appealing, I suppose we could
alternatively change hyp/entry.S to use adr_l for hyp_panic. Thoughts?

Sami

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On Fri, 05 Mar 2021 02:38:17 +0000,
Sami Tolvanen [off-list ref] wrote:

On Thu, Mar 4, 2021 at 2:34 PM Sami Tolvanen [off-list ref] wrote:

quoted

On Thu, Mar 4, 2021 at 2:17 PM Marc Zyngier [off-list ref] wrote:

quoted

On Thu, 04 Mar 2021 21:25:41 +0000,
Sami Tolvanen [off-list ref] wrote:

[...]

quoted

quoted

quoted

I assume hyp_panic() ends up being placed too far from __guest_enter()
when the kernel is large enough. Possibly something to do with LLVM
always splitting functions into separate sections with LTO. I'm not
sure why the linker cannot shuffle things around to make everyone
happy in this case, but I confirmed that this patch also fixes the
build issue for me:

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index af8e940d0f03..128197b7c794 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c

@@ -214,7 +214,7 @@ static void __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 }
 NOKPROBE_SYMBOL(__hyp_call_panic);

-void __noreturn hyp_panic(void)
+void __noreturn hyp_panic(void) __section(".text")
 {
        u64 spsr = read_sysreg_el2(SYS_SPSR);
        u64 elr = read_sysreg_el2(SYS_ELR);

We're getting into black-magic territory here. Why wouldn't hyp_panic
be in the .text section already?

It's not quite black magic. LLVM essentially flips on
-ffunction-sections with LTO and therefore, hyp_panic() will be in
.text.hyp_panic in vmlinux.o, while __guest_enter() will be in .text.
Everything ends up in .text when we link vmlinux, of course.

$ readelf --sections vmlinux.o | grep hyp_panic
  [3936] .text.hyp_panic   PROGBITS         0000000000000000  004b56e4

Note that disabling LTO here has essentially the same effect as using
__section(".text"). It stops the compiler from splitting these
functions into .text.* sections and makes it less likely that
hyp_panic() ends up too far away from __guest_enter().

If neither of these workarounds sound appealing, I suppose we could
alternatively change hyp/entry.S to use adr_l for hyp_panic. Thoughts?

That would be an actual fix instead of a workaround, as it would
remove existing assumptions about the relative locations of the two
objects. I guess you need to fix both instances with something such
as:

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index b0afad7a99c6..a43e1f7ee354 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S

@@ -85,8 +85,10 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
 
 	// If the hyp context is loaded, go straight to hyp_panic
 	get_loaded_vcpu x0, x1
-	cbz	x0, hyp_panic
-
+	cbnz	x0, 1f
+	adr_l	x0, hyp_panic
+	br	x0
+1:
 	// The hyp context is saved so make sure it is restored to allow
 	// hyp_panic to run at hyp and, subsequently, panic to run in the host.
 	// This makes use of __guest_exit to avoid duplication but sets the

@@ -94,7 +96,7 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
 	// current state is saved to the guest context but it will only be
 	// accurate if the guest had been completely restored.
 	adr_this_cpu x0, kvm_hyp_ctxt, x1
-	adr	x1, hyp_panic
+	adr_l	x1, hyp_panic
 	str	x1, [x0, #CPU_XREG_OFFSET(30)]
 
 	get_vcpu_ptr	x1, x0

which is completely untested. I wouldn't be surprised if there were
more of these somewhere.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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On Fri, 5 Mar 2021 at 12:38, Marc Zyngier [off-list ref] wrote:

Agree with replacing the conditional branches that refer to external
symbols: the compiler never emits those, for the reason we are seeing
here, i.e., the range is simply insufficient.

But let's just use 'b hyp_panic' instead, no?

A quick grep gives me

$ objdump -r vmlinux.o |grep BR19
000000000005b6e0 R_AARCH64_CONDBR19  hyp_panic
0000000000418e08 R_AARCH64_CONDBR19  __memcpy
0000000000418e14 R_AARCH64_CONDBR19  __memcpy
0000000000003818 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003898 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003918 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003998 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003a18 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003a98 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003b18 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003b98 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003c10 R_AARCH64_CONDBR19  __kvm_nvhe___host_exit
0000000000003c1c R_AARCH64_CONDBR19  __kvm_nvhe___host_exit
00000000000064f0 R_AARCH64_CONDBR19  __kvm_nvhe_hyp_panic
000000000000078c R_AARCH64_CONDBR19  __kvm_nvhe___kvm_handle_stub_hvc

So there are definitely a few other cases that require another look.

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On Fri, Mar 5, 2021 at 6:22 AM Ard Biesheuvel [off-list ref] wrote:

On Fri, 5 Mar 2021 at 12:38, Marc Zyngier [off-list ref] wrote:

quoted

On Fri, 05 Mar 2021 02:38:17 +0000,
Sami Tolvanen [off-list ref] wrote:

quoted

On Thu, Mar 4, 2021 at 2:34 PM Sami Tolvanen [off-list ref] wrote:

quoted

On Thu, Mar 4, 2021 at 2:17 PM Marc Zyngier [off-list ref] wrote:

quoted

On Thu, 04 Mar 2021 21:25:41 +0000,
Sami Tolvanen [off-list ref] wrote:

[...]

quoted

quoted

quoted

quoted

I assume hyp_panic() ends up being placed too far from __guest_enter()
when the kernel is large enough. Possibly something to do with LLVM
always splitting functions into separate sections with LTO. I'm not
sure why the linker cannot shuffle things around to make everyone
happy in this case, but I confirmed that this patch also fixes the
build issue for me:

diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
index af8e940d0f03..128197b7c794 100644
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c

@@ -214,7 +214,7 @@ static void __hyp_call_panic(u64 spsr, u64 elr, u64 par)
 }
 NOKPROBE_SYMBOL(__hyp_call_panic);

-void __noreturn hyp_panic(void)
+void __noreturn hyp_panic(void) __section(".text")
 {
        u64 spsr = read_sysreg_el2(SYS_SPSR);
        u64 elr = read_sysreg_el2(SYS_ELR);

We're getting into black-magic territory here. Why wouldn't hyp_panic
be in the .text section already?

It's not quite black magic. LLVM essentially flips on
-ffunction-sections with LTO and therefore, hyp_panic() will be in
.text.hyp_panic in vmlinux.o, while __guest_enter() will be in .text.
Everything ends up in .text when we link vmlinux, of course.

$ readelf --sections vmlinux.o | grep hyp_panic
  [3936] .text.hyp_panic   PROGBITS         0000000000000000  004b56e4

Note that disabling LTO here has essentially the same effect as using
__section(".text"). It stops the compiler from splitting these
functions into .text.* sections and makes it less likely that
hyp_panic() ends up too far away from __guest_enter().

If neither of these workarounds sound appealing, I suppose we could
alternatively change hyp/entry.S to use adr_l for hyp_panic. Thoughts?

That would be an actual fix instead of a workaround, as it would
remove existing assumptions about the relative locations of the two
objects. I guess you need to fix both instances with something such
as:

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index b0afad7a99c6..a43e1f7ee354 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S

@@ -85,8 +85,10 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)

        // If the hyp context is loaded, go straight to hyp_panic
        get_loaded_vcpu x0, x1
-       cbz     x0, hyp_panic
-
+       cbnz    x0, 1f
+       adr_l   x0, hyp_panic
+       br      x0
+1:

Agree with replacing the conditional branches that refer to external
symbols: the compiler never emits those, for the reason we are seeing
here, i.e., the range is simply insufficient.

But let's just use 'b hyp_panic' instead, no?

Alright, this seems to work for me:

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index b0afad7a99c6..c62265951467 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S

@@ -85,8 +85,10 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)

        // If the hyp context is loaded, go straight to hyp_panic
        get_loaded_vcpu x0, x1
-       cbz     x0, hyp_panic
+       cbnz    x0, 1f
+       b       hyp_panic

+1:
        // The hyp context is saved so make sure it is restored to allow
        // hyp_panic to run at hyp and, subsequently, panic to run in the host.
        // This makes use of __guest_exit to avoid duplication but sets the

@@ -94,7 +96,7 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
        // current state is saved to the guest context but it will only be
        // accurate if the guest had been completely restored.
        adr_this_cpu x0, kvm_hyp_ctxt, x1
-       adr     x1, hyp_panic
+       adr_l   x1, hyp_panic
        str     x1, [x0, #CPU_XREG_OFFSET(30)]

        get_vcpu_ptr    x1, x0

But when I say work, I mean this fixes the allmodconfig build with
LTO, and my kernel boots at EL2. I don't actually have a way to
properly test KVM on arm64. If nobody sees obvious issues here, I can
send a proper patch a bit later.

quoted

        // The hyp context is saved so make sure it is restored to allow
        // hyp_panic to run at hyp and, subsequently, panic to run in the host.
        // This makes use of __guest_exit to avoid duplication but sets the

@@ -94,7 +96,7 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
        // current state is saved to the guest context but it will only be
        // accurate if the guest had been completely restored.
        adr_this_cpu x0, kvm_hyp_ctxt, x1
-       adr     x1, hyp_panic
+       adr_l   x1, hyp_panic
        str     x1, [x0, #CPU_XREG_OFFSET(30)]

        get_vcpu_ptr    x1, x0

which is completely untested. I wouldn't be surprised if there were
more of these somewhere.

A quick grep gives me

$ objdump -r vmlinux.o |grep BR19
000000000005b6e0 R_AARCH64_CONDBR19  hyp_panic
0000000000418e08 R_AARCH64_CONDBR19  __memcpy
0000000000418e14 R_AARCH64_CONDBR19  __memcpy

These two are in __memmove. This shouldn't be an issue, at least with LTO.

0000000000003818 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003898 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003918 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003998 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003a18 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003a98 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003b18 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003b98 R_AARCH64_CONDBR19  __kvm_nvhe___guest_exit_panic
0000000000003c10 R_AARCH64_CONDBR19  __kvm_nvhe___host_exit
0000000000003c1c R_AARCH64_CONDBR19  __kvm_nvhe___host_exit
00000000000064f0 R_AARCH64_CONDBR19  __kvm_nvhe_hyp_panic
000000000000078c R_AARCH64_CONDBR19  __kvm_nvhe___kvm_handle_stub_hvc

It looks like all the nvhe code is linked together into kvm_nvhe.o, so
I don't think these will cause problems either.

Sami

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On 2021-03-05 16:55, Sami Tolvanen wrote:

Please do, it is "obviously correct"! ;-)

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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