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Message-ID: <46e5954c-a9a8-f4a8-07cc-de42e2753051@huawei.com>
Date: Thu, 19 May 2022 14:29:54 +0800
From: Tong Tiangen <tongtiangen@...wei.com>
To: Mark Rutland <mark.rutland@....com>
CC: James Morse <james.morse@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
"Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Robin Murphy <robin.murphy@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"Catalin Marinas" <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
"Alexander Viro" <viro@...iv.linux.org.uk>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>, <x86@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>, <linuxppc-dev@...ts.ozlabs.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Xie XiuQi <xiexiuqi@...wei.com>,
Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v4 3/7] arm64: add support for machine check error
safe
在 2022/5/13 23:26, Mark Rutland 写道:
> On Wed, Apr 20, 2022 at 03:04:14AM +0000, Tong Tiangen wrote:
>> During the processing of arm64 kernel hardware memory errors(do_sea()), if
>> the errors is consumed in the kernel, the current processing is panic.
>> However, it is not optimal.
>>
>> Take uaccess for example, if the uaccess operation fails due to memory
>> error, only the user process will be affected, kill the user process
>> and isolate the user page with hardware memory errors is a better choice.
>
> Conceptually, I'm fine with the idea of constraining what we do for a
> true uaccess, but I don't like the implementation of this at all, and I
> think we first need to clean up the arm64 extable usage to clearly
> distinguish a uaccess from another access.
OK,using EX_TYPE_UACCESS and this extable type could be recover, this is
more reasonable.
For EX_TYPE_UACCESS_ERR_ZERO, today we use it for kernel accesses in a
couple of cases, such as
get_user/futex/__user_cache_maint()/__user_swpX_asm(), your suggestion is:
get_user continues to use EX_TYPE_UACCESS_ERR_ZERO and the other cases
use new type EX_TYPE_FIXUP_ERR_ZERO?
Thanks,
Tong.
>
>> This patch only enable machine error check framework, it add exception
>> fixup before kernel panic in do_sea() and only limit the consumption of
>> hardware memory errors in kernel mode triggered by user mode processes.
>> If fixup successful, panic can be avoided.
>>
>> Consistent with PPC/x86, it is implemented by CONFIG_ARCH_HAS_COPY_MC.
>>
>> Also add copy_mc_to_user() in include/linux/uaccess.h, this helper is
>> called when CONFIG_ARCH_HAS_COPOY_MC is open.
>>
>> Signed-off-by: Tong Tiangen <tongtiangen@...wei.com>
>> ---
>> arch/arm64/Kconfig | 1 +
>> arch/arm64/include/asm/extable.h | 1 +
>> arch/arm64/mm/extable.c | 17 +++++++++++++++++
>> arch/arm64/mm/fault.c | 27 ++++++++++++++++++++++++++-
>> include/linux/uaccess.h | 9 +++++++++
>> 5 files changed, 54 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index d9325dd95eba..012e38309955 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -19,6 +19,7 @@ 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/extable.h b/arch/arm64/include/asm/extable.h
>> index 72b0e71cc3de..f80ebd0addfd 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_mc(struct pt_regs *regs);
>> #endif
>> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
>> index 489455309695..4f0083a550d4 100644
>> --- a/arch/arm64/mm/extable.c
>> +++ b/arch/arm64/mm/extable.c
>> @@ -9,6 +9,7 @@
>>
>> #include <asm/asm-extable.h>
>> #include <asm/ptrace.h>
>> +#include <asm/esr.h>
>>
>> static inline unsigned long
>> get_ex_fixup(const struct exception_table_entry *ex)
>> @@ -84,3 +85,19 @@ bool fixup_exception(struct pt_regs *regs)
>>
>> BUG();
>> }
>> +
>> +bool fixup_exception_mc(struct pt_regs *regs)
>> +{
>> + const struct exception_table_entry *ex;
>> +
>> + ex = search_exception_tables(instruction_pointer(regs));
>> + if (!ex)
>> + return false;
>> +
>> + /*
>> + * This is not complete, More Machine check safe extable type can
>> + * be processed here.
>> + */
>> +
>> + return false;
>> +}
>
> This is at best misnamed; It doesn't actually apply the fixup, it just
> searches for one.
Yeah, you're right about the current logic, so i added notes to explain
the scenarios that will be added later.
>
>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> index 77341b160aca..a9e6fb1999d1 100644
>> --- a/arch/arm64/mm/fault.c
>> +++ b/arch/arm64/mm/fault.c
>> @@ -695,6 +695,29 @@ static int do_bad(unsigned long far, unsigned int esr, struct pt_regs *regs)
>> return 1; /* "fault" */
>> }
>>
>> +static bool arm64_do_kernel_sea(unsigned long addr, unsigned int esr,
>> + struct pt_regs *regs, int sig, int code)
>> +{
>> + if (!IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC))
>> + return false;
>> +
>> + if (user_mode(regs) || !current->mm)
>> + return false;
>> +
>> + if (apei_claim_sea(regs) < 0)
>> + return false;
>> +
>> + if (!fixup_exception_mc(regs))
>> + return false;
>> +
>> + set_thread_esr(0, esr);
>> +
>> + arm64_force_sig_fault(sig, code, addr,
>> + "Uncorrected hardware memory error in kernel-access\n");
>> +
>> + return true;
>> +}
>> +
>> static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs)
>> {
>> const struct fault_info *inf;
>> @@ -720,7 +743,9 @@ static int do_sea(unsigned long far, unsigned int esr, struct pt_regs *regs)
>> */
>> siaddr = untagged_addr(far);
>> }
>> - arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr);
>> +
>> + if (!arm64_do_kernel_sea(siaddr, esr, regs, inf->sig, inf->code))
>> + arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr);
>>
>> return 0;
>> }
>> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
>> index 546179418ffa..884661b29c17 100644
>> --- a/include/linux/uaccess.h
>> +++ b/include/linux/uaccess.h
>> @@ -174,6 +174,15 @@ copy_mc_to_kernel(void *dst, const void *src, size_t cnt)
>> }
>> #endif
>>
>> +#ifndef copy_mc_to_user
>> +static inline unsigned long __must_check
>> +copy_mc_to_user(void *dst, const void *src, size_t cnt)
>> +{
>> + check_object_size(src, cnt, true);
>> + return raw_copy_to_user(dst, src, cnt);
>> +}
>> +#endif
>
> Why do we need a special copy_mc_to_user() ?
>
> Why are we not making *every* true uaccess recoverable? That way the
> regular copy_to_user() would just work.
Agreed, will fixed next version.
Thanks,
Tong.
>
> Thanks,
> Mark.
> .
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