Date:   Thu, 7 Apr 2022 22:56:00 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [RFC PATCH -next V2 7/7] arm64: add pagecache reading to machine
 check safe



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@...wei.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@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> .

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