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

Tong Tiangen
2024-08-20T02:43:13Z

在 2024/8/19 18:30, Jonathan Cameron 写道:
> On Tue, 28 May 2024 16:59:11 +0800
> Tong Tiangen <tongtiangen@huawei.com> 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 <tongtiangen@huawei.com>
>
> Hi - this is going slow :(
>
> A few comments inline in the meantime but this really needs ARM maintainers
> to take a (hopefully final) look.
>
> Jonathan
>
>
>> 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
>
> Does anyone care enough about the alignment to bother realigning for one
> long line? I'd be tempted not to bother, but up to maintainers.
>
>
>> 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
>> @@ -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])
>
> Alignment looks off?

Hi, Jonathan:

How about we change this in conjunction with mark's suggestion? :)

>
>> USER(9998f, sttrb tmp1w, [dst])
>> add dst, dst, #1
>> 9998: sub x0, end, dst // bytes not copied
>
>
>
>> 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))
>
> I'd keep to the the (apei_claim_sea(regs) == 0)
> used in the original code. That hints to the reader that we are
> interested here in an 'error' code rather than apei_claim_sea() returning
> a bool. I initially wondered why we return true when the code
> fails to claim it.
>
> Also, perhaps if you return 0 for success and an error code if not
> you could just make this
>
> if (user_mode(regs))
> return apei_claim_sea(regs);
>
> if (IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) {
> if (fixup_exception_me(regs)) {
> return apei_claim_sea(regs);
> }
> }
>
> return false;
>
> or maybe even (I may have messed this up, but I think this logic
> works).
>
> if (!user_mode(regs) && IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) {
> if (!fixup_exception_me(regs))
> return false;
> }
> return apei_claim_sea(regs);
>
>
>> + return true;
>> + } else if (IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) {
>> + if (fixup_exception_me(regs) && !apei_claim_sea(regs))
>
> Same here with using apei_claim_sea(regs) == 0 so it's obvious we
> are checking for an error, not a boolean.
>
>> + return true;
>> + }
>> +
>> + return false;
>> +}
>> +
>> 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))
>
> It might be made sense to factor this out first, then could be reviewed
> as a noop before the new stuff is added. Still it's not much code, so doesn't
> really matter.
> Might be worth keeping to returning 0 for success, error code
> otherwise as per apei_claim_sea(regs)
>
> The bool returning functions in the nearby code tend to be is_xxxx
> not things that succeed or not.
>
> If you change it to return int make this
> if (do_apei_claim_sea(regs) == 0)
> so it's obvious this is the no error case.
>

My fault, treating the return value of apei_claim_sea() as bool has
caused some confusion. Perhaps using "== 0" can reduce this confuse.

Here's the change:

static int do_apei_claim_sea(struct pt_regs *regs)
{
if (!user_mode(regs) && IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) {
if (!fixup_exception_me(regs)))
return -ENOENT;
}

return apei_claim_sea(regs);
}

static int do_sea(...)
{
[...]
if (do_apei_claim_sea(regs) == 0)
return 0;
[...]
}

I'll modify it later with the comments of mark.

Thanks,
Tong.

>> return 0;
>> - }
>>
>> + inf = esr_to_fault_info(esr);
>> if (esr & ESR_ELx_FnV) {
>> siaddr = 0;
>> } else {
>
> .