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SubjectRe: [RFC PATCH -next V2 7/7] arm64: add pagecache reading to machine check safe
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在 2022/4/6 19:27, Mark Rutland 写道:
> On Wed, Apr 06, 2022 at 09:13:11AM +0000, Tong Tiangen wrote:
>> When user process reading file, the data is cached in pagecache and
>> the data belongs to the user process, When machine check error is
>> encountered during pagecache reading, killing the user process and
>> isolate the user page with hardware memory errors is a more reasonable
>> choice than kernel panic.
>>
>> The __arch_copy_mc_to_user() in copy_to_user_mc.S is largely borrows
>> from __arch_copy_to_user() in copy_to_user.S and the main difference
>> is __arch_copy_mc_to_user() add the extable entry to support machine
>> check safe.
>
> As with prior patches, *why* is the distinction necessary?
>
> This patch adds a bunch of conditional logic, but *structurally* it doesn't
> alter the handling to be substantially different for the MC and non-MC cases.
>
> This seems like pointless duplication that just makes it harder to maintain
> this code.
>
> Thanks,
> Mark.

Agreed, The implementation here looks a little ugly and harder to maintain.

The purpose of my doing this is not all copy_to_user can be recovered.

A memory error is consumed when reading pagecache using copy_to_user.
I think in this scenario, only the process is affected because it can't read
pagecache data correctly. Just kill the process and don't need the whole
kernel panic.

So I need two different copy_to_user implementation, one is existing
__arch_copy_to_user,
this function will panic when consuming memory errors. The other one is
this new helper
__arch_copy_mc_to_user, this interface is used when reading pagecache.
It can recover from
consume memory error.

In future, if find a scenario use copy_to_user can also be recovered, we
can also use this mc
safe helper instead it.

Thanks,
Tong.

>
>> In _copy_page_to_iter(), machine check safe only considered ITER_IOVEC
>> which is used by pagecache reading.
>>
>> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
>> ---
>> arch/arm64/include/asm/uaccess.h | 15 ++++++
>> arch/arm64/lib/Makefile | 2 +-
>> arch/arm64/lib/copy_to_user_mc.S | 78 +++++++++++++++++++++++++++++
>> include/linux/uio.h | 9 +++-
>> lib/iov_iter.c | 85 +++++++++++++++++++++++++-------
>> 5 files changed, 170 insertions(+), 19 deletions(-)
>> create mode 100644 arch/arm64/lib/copy_to_user_mc.S
>>
>> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
>> index 24b662407fbd..f0d5e811165a 100644
>> --- a/arch/arm64/include/asm/uaccess.h
>> +++ b/arch/arm64/include/asm/uaccess.h
>> @@ -448,6 +448,21 @@ extern long strncpy_from_user(char *dest, const char __user *src, long count);
>>
>> extern __must_check long strnlen_user(const char __user *str, long n);
>>
>> +#ifdef CONFIG_ARCH_HAS_COPY_MC
>> +extern unsigned long __must_check __arch_copy_mc_to_user(void __user *to,
>> + const void *from, unsigned long n);
>> +static inline unsigned long __must_check
>> +copy_mc_to_user(void __user *to, const void *from, unsigned long n)
>> +{
>> + uaccess_ttbr0_enable();
>> + n = __arch_copy_mc_to_user(__uaccess_mask_ptr(to), from, n);
>> + uaccess_ttbr0_disable();
>> +
>> + return n;
>> +}
>> +#define copy_mc_to_user copy_mc_to_user
>> +#endif
>> +
>> #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
>> struct page;
>> void memcpy_page_flushcache(char *to, struct page *page, size_t offset, size_t len);
>> diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
>> index 29c578414b12..9b3571227fb4 100644
>> --- a/arch/arm64/lib/Makefile
>> +++ b/arch/arm64/lib/Makefile
>> @@ -23,4 +23,4 @@ obj-$(CONFIG_ARM64_MTE) += mte.o
>>
>> obj-$(CONFIG_KASAN_SW_TAGS) += kasan_sw_tags.o
>>
>> -obj-$(CONFIG_ARCH_HAS_CPY_MC) += copy_page_mc.o
>> +obj-$(CONFIG_ARCH_HAS_COPY_MC) += copy_page_mc.o copy_to_user_mc.o
>> diff --git a/arch/arm64/lib/copy_to_user_mc.S b/arch/arm64/lib/copy_to_user_mc.S
>> new file mode 100644
>> index 000000000000..9d228ff15446
>> --- /dev/null
>> +++ b/arch/arm64/lib/copy_to_user_mc.S
>> @@ -0,0 +1,78 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2012 ARM Ltd.
>> + */
>> +
>> +#include <linux/linkage.h>
>> +
>> +#include <asm/asm-uaccess.h>
>> +#include <asm/assembler.h>
>> +#include <asm/cache.h>
>> +
>> +/*
>> + * Copy to user space from a kernel buffer (alignment handled by the hardware)
>> + *
>> + * Parameters:
>> + * x0 - to
>> + * x1 - from
>> + * x2 - n
>> + * Returns:
>> + * x0 - bytes not copied
>> + */
>> + .macro ldrb1 reg, ptr, val
>> + 1000: ldrb \reg, [\ptr], \val;
>> + _asm_extable_mc 1000b, 9998f;
>> + .endm
>> +
>> + .macro strb1 reg, ptr, val
>> + user_ldst_mc 9998f, sttrb, \reg, \ptr, \val
>> + .endm
>> +
>> + .macro ldrh1 reg, ptr, val
>> + 1001: ldrh \reg, [\ptr], \val;
>> + _asm_extable_mc 1001b, 9998f;
>> + .endm
>> +
>> + .macro strh1 reg, ptr, val
>> + user_ldst_mc 9997f, sttrh, \reg, \ptr, \val
>> + .endm
>> +
>> + .macro ldr1 reg, ptr, val
>> + 1002: ldr \reg, [\ptr], \val;
>> + _asm_extable_mc 1002b, 9998f;
>> + .endm
>> +
>> + .macro str1 reg, ptr, val
>> + user_ldst_mc 9997f, sttr, \reg, \ptr, \val
>> + .endm
>> +
>> + .macro ldp1 reg1, reg2, ptr, val
>> + 1003: ldp \reg1, \reg2, [\ptr], \val;
>> + _asm_extable_mc 1003b, 9998f;
>> + .endm
>> +
>> + .macro stp1 reg1, reg2, ptr, val
>> + user_stp 9997f, \reg1, \reg2, \ptr, \val
>> + .endm
>> +
>> +end .req x5
>> +srcin .req x15
>> +SYM_FUNC_START(__arch_copy_mc_to_user)
>> + add end, x0, x2
>> + mov srcin, x1
>> +#include "copy_template.S"
>> + mov x0, #0
>> + ret
>> +
>> + // Exception fixups
>> +9997: cbz x0, 9998f // Check machine check exception
>> + cmp dst, dstin
>> + b.ne 9998f
>> + // Before being absolutely sure we couldn't copy anything, try harder
>> + ldrb tmp1w, [srcin]
>> +USER(9998f, sttrb tmp1w, [dst])
>> + add dst, dst, #1
>> +9998: sub x0, end, dst // bytes not copied
>> + ret
>> +SYM_FUNC_END(__arch_copy_mc_to_user)
>> +EXPORT_SYMBOL(__arch_copy_mc_to_user)
>> diff --git a/include/linux/uio.h b/include/linux/uio.h
>> index 739285fe5a2f..539d9ee9b032 100644
>> --- a/include/linux/uio.h
>> +++ b/include/linux/uio.h
>> @@ -147,10 +147,17 @@ size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
>> size_t _copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
>> size_t _copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i);
>>
>> +#ifdef CONFIG_ARCH_HAS_COPY_MC
>> +size_t copy_mc_page_to_iter(struct page *page, size_t offset, size_t bytes,
>> + struct iov_iter *i);
>> +#else
>> +#define copy_mc_page_to_iter copy_page_to_iter
>> +#endif
>> +
>> static inline size_t copy_folio_to_iter(struct folio *folio, size_t offset,
>> size_t bytes, struct iov_iter *i)
>> {
>> - return copy_page_to_iter(&folio->page, offset, bytes, i);
>> + return copy_mc_page_to_iter(&folio->page, offset, bytes, i);
>> }
>>
>> static __always_inline __must_check
>> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
>> index 6dd5330f7a99..2c5f3bb6391d 100644
>> --- a/lib/iov_iter.c
>> +++ b/lib/iov_iter.c
>> @@ -157,6 +157,19 @@ static int copyout(void __user *to, const void *from, size_t n)
>> return n;
>> }
>>
>> +#ifdef CONFIG_ARCH_HAS_COPY_MC
>> +static int copyout_mc(void __user *to, const void *from, size_t n)
>> +{
>> + if (access_ok(to, n)) {
>> + instrument_copy_to_user(to, from, n);
>> + n = copy_mc_to_user((__force void *) to, from, n);
>> + }
>> + return n;
>> +}
>> +#else
>> +#define copyout_mc copyout
>> +#endif
>> +
>> static int copyin(void *to, const void __user *from, size_t n)
>> {
>> if (should_fail_usercopy())
>> @@ -169,7 +182,7 @@ static int copyin(void *to, const void __user *from, size_t n)
>> }
>>
>> static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
>> - struct iov_iter *i)
>> + struct iov_iter *i, bool mc_safe)
>> {
>> size_t skip, copy, left, wanted;
>> const struct iovec *iov;
>> @@ -194,7 +207,10 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
>> from = kaddr + offset;
>>
>> /* first chunk, usually the only one */
>> - left = copyout(buf, from, copy);
>> + if (mc_safe)
>> + left = copyout_mc(buf, from, copy);
>> + else
>> + left = copyout(buf, from, copy);
>> copy -= left;
>> skip += copy;
>> from += copy;
>> @@ -204,7 +220,10 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
>> iov++;
>> buf = iov->iov_base;
>> copy = min(bytes, iov->iov_len);
>> - left = copyout(buf, from, copy);
>> + if (mc_safe)
>> + left = copyout_mc(buf, from, copy);
>> + else
>> + left = copyout(buf, from, copy);
>> copy -= left;
>> skip = copy;
>> from += copy;
>> @@ -223,7 +242,10 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
>>
>> kaddr = kmap(page);
>> from = kaddr + offset;
>> - left = copyout(buf, from, copy);
>> + if (mc_safe)
>> + left = copyout_mc(buf, from, copy);
>> + else
>> + left = copyout(buf, from, copy);
>> copy -= left;
>> skip += copy;
>> from += copy;
>> @@ -232,7 +254,10 @@ static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t b
>> iov++;
>> buf = iov->iov_base;
>> copy = min(bytes, iov->iov_len);
>> - left = copyout(buf, from, copy);
>> + if (mc_safe)
>> + left = copyout_mc(buf, from, copy);
>> + else
>> + left = copyout(buf, from, copy);
>> copy -= left;
>> skip = copy;
>> from += copy;
>> @@ -674,15 +699,6 @@ size_t _copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
>> EXPORT_SYMBOL(_copy_to_iter);
>>
>> #ifdef CONFIG_ARCH_HAS_COPY_MC
>> -static int copyout_mc(void __user *to, const void *from, size_t n)
>> -{
>> - if (access_ok(to, n)) {
>> - instrument_copy_to_user(to, from, n);
>> - n = copy_mc_to_user((__force void *) to, from, n);
>> - }
>> - return n;
>> -}
>> -
>> static size_t copy_mc_pipe_to_iter(const void *addr, size_t bytes,
>> struct iov_iter *i)
>> {
>> @@ -846,10 +862,10 @@ static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
>> }
>>
>> static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
>> - struct iov_iter *i)
>> + struct iov_iter *i, bool mc_safe)
>> {
>> if (likely(iter_is_iovec(i)))
>> - return copy_page_to_iter_iovec(page, offset, bytes, i);
>> + return copy_page_to_iter_iovec(page, offset, bytes, i, mc_safe);
>> if (iov_iter_is_bvec(i) || iov_iter_is_kvec(i) || iov_iter_is_xarray(i)) {
>> void *kaddr = kmap_local_page(page);
>> size_t wanted = _copy_to_iter(kaddr + offset, bytes, i);
>> @@ -878,7 +894,7 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
>> offset %= PAGE_SIZE;
>> while (1) {
>> size_t n = __copy_page_to_iter(page, offset,
>> - min(bytes, (size_t)PAGE_SIZE - offset), i);
>> + min(bytes, (size_t)PAGE_SIZE - offset), i, false);
>> res += n;
>> bytes -= n;
>> if (!bytes || !n)
>> @@ -893,6 +909,41 @@ size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
>> }
>> EXPORT_SYMBOL(copy_page_to_iter);
>>
>> +#ifdef CONFIG_ARCH_HAS_COPY_MC
>> +/**
>> + * copy_mc_page_to_iter - copy page to iter with source memory error exception handling.
>> + *
>> + * The filemap_read deploys this for pagecache reading and the main differences between
>> + * this and typical copy_page_to_iter() is call __copy_page_to_iter with mc_safe true.
>> + *
>> + * Return: number of bytes copied (may be %0)
>> + */
>> +size_t copy_mc_page_to_iter(struct page *page, size_t offset, size_t bytes,
>> + struct iov_iter *i)
>> +{
>> + size_t res = 0;
>> +
>> + if (unlikely(!page_copy_sane(page, offset, bytes)))
>> + return 0;
>> + page += offset / PAGE_SIZE; // first subpage
>> + offset %= PAGE_SIZE;
>> + while (1) {
>> + size_t n = __copy_page_to_iter(page, offset,
>> + min(bytes, (size_t)PAGE_SIZE - offset), i, true);
>> + res += n;
>> + bytes -= n;
>> + if (!bytes || !n)
>> + break;
>> + offset += n;
>> + if (offset == PAGE_SIZE) {
>> + page++;
>> + offset = 0;
>> + }
>> + }
>> + return res;
>> +}
>> +#endif
>> +
>> size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
>> struct iov_iter *i)
>> {
>> --
>> 2.18.0.huawei.25
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> .

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