On Mon, 29 Mar 2021 11:22:00 +0100,
Will Deacon [off-list ref] wrote:

On Fri, Mar 26, 2021 at 11:20:18AM +0000, Marc Zyngier wrote:

quoted

I guess I could either make this code conditional on CONFIG_ARM64_VHE
and let the machine crash early without a word, or have some later
checks once the machine started booting. In the later case, displaying
anything useful is going to be a challenge though (the odds of someone
having a serial console on this box are close to nil). Pick your poison.

I think the best thing to do would be to fail to initialise KVM if the
kernel is stuck at EL2 but we don't have VHE support compiled in. Is that
do-able?

To quote someone, it is "a little ugly on the side".

I came up with the following hack. Can't say I'm in love with it,
specially the sprinkling of checks in the alternative callbacks, but
hey, I can boot the machine without CONFIG_ARM64_VHE, and get the
expected splat at boot time:

[    0.033604] ------------[ cut here ]------------
[    0.033850] CPU: CPUs started in inconsistent modes
[    0.033854] WARNING: CPU: 0 PID: 1 at arch/arm64/kernel/smp.c:434 hyp_mode_check+0x90/0xc4
[    0.034863] Modules linked in:
[    0.035100] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.12.0-rc3-00103-geee3f110c447-dirty #3231
[    0.035776] Hardware name: Apple Mac mini (M1, 2020) (DT)
[    0.036192] pstate: 60400009 (nZCv daif +PAN -UAO -TCO BTYPE=--)
[    0.036654] pc : hyp_mode_check+0x90/0xc4
[    0.036963] lr : hyp_mode_check+0x90/0xc4
[    0.037271] sp : ffff800010053e30
[    0.037526] x29: ffff800010053e30 x28: 0000000000000000 
[    0.037935] x27: 0000000000000000 x26: 0000000000000000 
[    0.038344] x25: 0000000000000000 x24: 0000000000000000 
[    0.038754] x23: 0000000000000000 x22: 0000000000000000 
[    0.039163] x21: 0000000000000000 x20: ffffca3b2f53fc04 
[    0.039572] x19: ffffca3b2fac1000 x18: 0000000000000001 
[    0.039981] x17: 00000000cc4379d6 x16: 000000005c7b6156 
[    0.040391] x15: 0000000000000030 x14: ffffffffffffffff 
[    0.040800] x13: ffff800090053ab7 x12: ffff800010053ac0 
[    0.041209] x11: 0000000bbe2c6238 x10: ffffca3b2faa0ad8 
[    0.041618] x9 : ffffca3b2e310df0 x8 : fffffffffffe18b8 
[    0.042027] x7 : ffffca3b2fa481d8 x6 : 0000000000002ffd 
[    0.042437] x5 : 0000000000000000 x4 : 0000000000000000 
[    0.042846] x3 : 00000000ffffffff x2 : 0000000000000000 
[    0.043255] x1 : 0000000000000000 x0 : ffff4af181631280 
[    0.043665] Call trace:
[    0.043852]  hyp_mode_check+0x90/0xc4
[    0.044134]  smp_cpus_done+0x34/0x48
[    0.044409]  smp_init+0x80/0x90
[    0.044651]  kernel_init_freeable+0x108/0x160
[    0.044986]  kernel_init+0x20/0x12c
[    0.045254]  ret_from_fork+0x10/0x3c
[    0.045530] ---[ end trace 0736417247c9e9a3 ]---
[...]
[    0.616800] kvm [1]: HYP mode not available

I'll wrap that up in a separate patch, and we can then discuss whether
we really want it...

Thanks,

	M.

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 7379f35ae2c6..69bc4e26aa26 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h

@@ -72,6 +72,11 @@ void __hyp_reset_vectors(void);
 
 DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 
+static inline bool is_kernel_in_hyp_mode(void)
+{
+	return read_sysreg(CurrentEL) == CurrentEL_EL2;
+}
+
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {

@@ -83,6 +88,10 @@ static inline bool is_hyp_mode_available(void)
 	    static_branch_likely(&kvm_protected_mode_initialized))
 		return true;
 
+	/* Catch braindead CPUs */
+	if (!IS_ENABLED(CONFIG_ARM64_VHE) && is_kernel_in_hyp_mode())
+		return false;
+
 	return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
 		__boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
 }

@@ -98,12 +107,11 @@ static inline bool is_hyp_mode_mismatched(void)
 	    static_branch_likely(&kvm_protected_mode_initialized))
 		return false;
 
-	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
-}
+	/* Catch braindead CPUs */
+	if (!IS_ENABLED(CONFIG_ARM64_VHE) && is_kernel_in_hyp_mode())
+		return true;
 
-static inline bool is_kernel_in_hyp_mode(void)
-{
-	return read_sysreg(CurrentEL) == CurrentEL_EL2;
+	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
 }
 
 static __always_inline bool has_vhe(void)

diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index 978301392d67..edb048654e00 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c

@@ -156,6 +156,9 @@ void __init kvm_update_va_mask(struct alt_instr *alt,
 {
 	int i;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 5);
 
 	for (i = 0; i < nr_inst; i++) {

@@ -191,6 +194,9 @@ void kvm_patch_vector_branch(struct alt_instr *alt,
 	u64 addr;
 	u32 insn;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 4);
 
 	if (!cpus_have_const_cap(ARM64_SPECTRE_V3A) || WARN_ON_ONCE(has_vhe()))

@@ -244,6 +250,9 @@ static void generate_mov_q(u64 val, __le32 *origptr, __le32 *updptr, int nr_inst
 {
 	u32 insn, oinsn, rd;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 4);
 
 	/* Compute target register */

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

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