Re: [PATCH v12 2/6] arm64: add support for ARCH_HAS_COPY_MC

From: Mark Rutland <mark.rutland@arm.com>
Date: 2024-08-19 17:29:29
Also in: linux-arm-kernel, linux-mm, lkml

Hi Tong,

On Tue, May 28, 2024 at 04:59:11PM +0800, Tong Tiangen wrote:

For the arm64 kernel, when it processes hardware memory errors for
synchronize notifications(do_sea()), if the errors is consumed within the
kernel, the current processing is panic. However, it is not optimal.

Take copy_from/to_user for example, If ld* triggers a memory error, even in
kernel mode, only the associated process is affected. Killing the user
process and isolating the corrupt page is a better choice.

New fixup type EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE is added to identify insn
that can recover from memory errors triggered by access to kernel memory.

Signed-off-by: Tong Tiangen <redacted>

Generally this looks ok, but I have a couple of comments below.

quoted hunk ↗ jump to hunk

---
 arch/arm64/Kconfig                   |  1 +
 arch/arm64/include/asm/asm-extable.h | 31 +++++++++++++++++++++++-----
 arch/arm64/include/asm/asm-uaccess.h |  4 ++++
 arch/arm64/include/asm/extable.h     |  1 +
 arch/arm64/lib/copy_to_user.S        | 10 ++++-----
 arch/arm64/mm/extable.c              | 19 +++++++++++++++++
 arch/arm64/mm/fault.c                | 27 +++++++++++++++++-------
 7 files changed, 75 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 5d91259ee7b5..13ca06ddf3dd 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -20,6 +20,7 @@ config ARM64
 	select ARCH_ENABLE_SPLIT_PMD_PTLOCK if PGTABLE_LEVELS > 2
 	select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
 	select ARCH_HAS_CACHE_LINE_SIZE
+	select ARCH_HAS_COPY_MC if ACPI_APEI_GHES
 	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_DEBUG_VIRTUAL
 	select ARCH_HAS_DEBUG_VM_PGTABLE

diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
index 980d1dd8e1a3..9c0664fe1eb1 100644
--- a/arch/arm64/include/asm/asm-extable.h
+++ b/arch/arm64/include/asm/asm-extable.h

@@ -5,11 +5,13 @@
 #include <linux/bits.h>
 #include <asm/gpr-num.h>
 
-#define EX_TYPE_NONE			0
-#define EX_TYPE_BPF			1
-#define EX_TYPE_UACCESS_ERR_ZERO	2
-#define EX_TYPE_KACCESS_ERR_ZERO	3
-#define EX_TYPE_LOAD_UNALIGNED_ZEROPAD	4
+#define EX_TYPE_NONE				0
+#define EX_TYPE_BPF				1
+#define EX_TYPE_UACCESS_ERR_ZERO		2
+#define EX_TYPE_KACCESS_ERR_ZERO		3
+#define EX_TYPE_LOAD_UNALIGNED_ZEROPAD		4
+/* kernel access memory error safe */
+#define EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE	5

Could we please use 'MEM_ERR', and likewise for the macros below? That's
more obvious than 'ME_SAFE', and we wouldn't need the comment here.
Likewise elsewhere in this patch and the series.

To Jonathan's comment, I do prefer these numbers are aligned, so aside
from the naming, the diff above looks good.

quoted hunk ↗ jump to hunk

 
 /* Data fields for EX_TYPE_UACCESS_ERR_ZERO */
 #define EX_DATA_REG_ERR_SHIFT	0

@@ -51,6 +53,17 @@
 #define _ASM_EXTABLE_UACCESS(insn, fixup)				\
 	_ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, wzr, wzr)
 
+#define _ASM_EXTABLE_KACCESS_ERR_ZERO_ME_SAFE(insn, fixup, err, zero)	\
+	__ASM_EXTABLE_RAW(insn, fixup, 					\
+			  EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE,		\
+			  (						\
+			    EX_DATA_REG(ERR, err) |			\
+			    EX_DATA_REG(ZERO, zero)			\
+			  ))
+
+#define _ASM_EXTABLE_KACCESS_ME_SAFE(insn, fixup)			\
+	_ASM_EXTABLE_KACCESS_ERR_ZERO_ME_SAFE(insn, fixup, wzr, wzr)
+
 /*
  * Create an exception table entry for uaccess `insn`, which will branch to `fixup`
  * when an unhandled fault is taken.
@@ -69,6 +82,14 @@
 	.endif
 	.endm
 
+/*
+ * Create an exception table entry for kaccess me(memory error) safe `insn`, which
+ * will branch to `fixup` when an unhandled fault is taken.
+ */
+	.macro          _asm_extable_kaccess_me_safe, insn, fixup
+	_ASM_EXTABLE_KACCESS_ME_SAFE(\insn, \fixup)
+	.endm
+

With the naming above, I think this can be:

| /*
|  * Create an exception table entry for kaccess `insn`, which will branch to
|  * `fixup` when a memory error is taken
|  */
| 	.macro		_asm_extable_kaccess_mem_err, insn, fixup
| 	_ASM_EXTABLE_KACCESS_MEM_ERR(\insn, \fixup)
| 	.endm

quoted hunk ↗ jump to hunk

 #else /* __ASSEMBLY__ */
 
 #include <linux/stringify.h>

diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
index 5b6efe8abeeb..7bbebfa5b710 100644
--- a/arch/arm64/include/asm/asm-uaccess.h
+++ b/arch/arm64/include/asm/asm-uaccess.h

@@ -57,6 +57,10 @@ alternative_else_nop_endif
 	.endm
 #endif
 
+#define KERNEL_ME_SAFE(l, x...)			\
+9999:	x;					\
+	_asm_extable_kaccess_me_safe	9999b, l
+
 #define USER(l, x...)				\
 9999:	x;					\
 	_asm_extable_uaccess	9999b, l

diff --git a/arch/arm64/include/asm/extable.h b/arch/arm64/include/asm/extable.h
index 72b0e71cc3de..bc49443bc502 100644
--- a/arch/arm64/include/asm/extable.h
+++ b/arch/arm64/include/asm/extable.h

@@ -46,4 +46,5 @@ bool ex_handler_bpf(const struct exception_table_entry *ex,
 #endif /* !CONFIG_BPF_JIT */
 
 bool fixup_exception(struct pt_regs *regs);
+bool fixup_exception_me(struct pt_regs *regs);
 #endif

diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 802231772608..2ac716c0d6d8 100644
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S

@@ -20,7 +20,7 @@
  *	x0 - bytes not copied
  */
 	.macro ldrb1 reg, ptr, val
-	ldrb  \reg, [\ptr], \val
+	KERNEL_ME_SAFE(9998f, ldrb  \reg, [\ptr], \val)
 	.endm
 
 	.macro strb1 reg, ptr, val

@@ -28,7 +28,7 @@
 	.endm
 
 	.macro ldrh1 reg, ptr, val
-	ldrh  \reg, [\ptr], \val
+	KERNEL_ME_SAFE(9998f, ldrh  \reg, [\ptr], \val)
 	.endm
 
 	.macro strh1 reg, ptr, val

@@ -36,7 +36,7 @@
 	.endm
 
 	.macro ldr1 reg, ptr, val
-	ldr \reg, [\ptr], \val
+	KERNEL_ME_SAFE(9998f, ldr \reg, [\ptr], \val)
 	.endm
 
 	.macro str1 reg, ptr, val

@@ -44,7 +44,7 @@
 	.endm
 
 	.macro ldp1 reg1, reg2, ptr, val
-	ldp \reg1, \reg2, [\ptr], \val
+	KERNEL_ME_SAFE(9998f, ldp \reg1, \reg2, [\ptr], \val)
 	.endm
 
 	.macro stp1 reg1, reg2, ptr, val

These changes mean that regular copy_to_user() will handle kernel memory
errors, rather than only doing that in copy_mc_to_user(). If that's
intentional, please call that out explicitly in the commit message.

quoted hunk ↗ jump to hunk

@@ -64,7 +64,7 @@ SYM_FUNC_START(__arch_copy_to_user)
 9997:	cmp	dst, dstin
 	b.ne	9998f
 	// Before being absolutely sure we couldn't copy anything, try harder
-	ldrb	tmp1w, [srcin]
+KERNEL_ME_SAFE(9998f, ldrb	tmp1w, [srcin])
 USER(9998f, sttrb tmp1w, [dst])
 	add	dst, dst, #1
 9998:	sub	x0, end, dst			// bytes not copied

Same comment as above.

quoted hunk ↗ jump to hunk

diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
index 228d681a8715..8c690ae61944 100644
--- a/arch/arm64/mm/extable.c
+++ b/arch/arm64/mm/extable.c

@@ -72,7 +72,26 @@ bool fixup_exception(struct pt_regs *regs)
 		return ex_handler_uaccess_err_zero(ex, regs);
 	case EX_TYPE_LOAD_UNALIGNED_ZEROPAD:
 		return ex_handler_load_unaligned_zeropad(ex, regs);
+	case EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE:
+		return false;
 	}
 
 	BUG();
 }
+
+bool fixup_exception_me(struct pt_regs *regs)
+{
+	const struct exception_table_entry *ex;
+
+	ex = search_exception_tables(instruction_pointer(regs));
+	if (!ex)
+		return false;
+
+	switch (ex->type) {
+	case EX_TYPE_UACCESS_ERR_ZERO:
+	case EX_TYPE_KACCESS_ERR_ZERO_ME_SAFE:
+		return ex_handler_uaccess_err_zero(ex, regs);
+	}
+
+	return false;
+}

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 451ba7cbd5ad..2dc65f99d389 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c

@@ -708,21 +708,32 @@ static int do_bad(unsigned long far, unsigned long esr, struct pt_regs *regs)
 	return 1; /* "fault" */
 }
 
+/*
+ * APEI claimed this as a firmware-first notification.
+ * Some processing deferred to task_work before ret_to_user().
+ */
+static bool do_apei_claim_sea(struct pt_regs *regs)
+{
+	if (user_mode(regs)) {
+		if (!apei_claim_sea(regs))
+			return true;
+	} else if (IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) {
+		if (fixup_exception_me(regs) && !apei_claim_sea(regs))
+			return true;
+	}
+
+	return false;
+}

Hmm... that'll fixup the exception even if we don't manage to claim a
the SEA. I suspect this should probably be:

static bool do_apei_claim_sea(struct pt_regs *regs)
{
	if (apei_claim_sea(regs))
		return false;
	if (user_mode(regs))
		return true;
	if (IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC))
		return !fixup_excepton_mem_err(regs);
	
	return false;
}

... unless we *don't* want to claim the SEA in the case we don't have a
fixup?

Mark.

+
 static int do_sea(unsigned long far, unsigned long esr, struct pt_regs *regs)
 {
 	const struct fault_info *inf;
 	unsigned long siaddr;
 
-	inf = esr_to_fault_info(esr);
-
-	if (user_mode(regs) && apei_claim_sea(regs) == 0) {
-		/*
-		 * APEI claimed this as a firmware-first notification.
-		 * Some processing deferred to task_work before ret_to_user().
-		 */
+	if (do_apei_claim_sea(regs))
 		return 0;
-	}
 
+	inf = esr_to_fault_info(esr);
 	if (esr & ESR_ELx_FnV) {
 		siaddr = 0;
 	} else {
-- 
2.25.1

`h`	back out one level
`j`	next message in thread
`k`	previous message in thread
`l`	drill in
`Esc`	close help / fold thread tree
`?`	toggle this help