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    Subject[PATCH v3 3/9] x86, memcpy_mcsafe: return bytes remaining
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    Date
    Machine check safe memory copies are currently deployed in the pmem
    driver whenever reading from persistent memory media, so that -EIO is
    returned rather than triggering a kernel panic. While this protects most
    pmem accesses, it is not complete in the filesystem-dax case. When
    filesystem-dax is enabled reads may bypass the block layer and the
    driver via dax_iomap_actor() and its usage of copy_to_iter().

    In preparation for creating a copy_to_iter() variant that can handle
    machine checks, teach memcpy_mcsafe() to return the number of bytes
    remaining rather than -EFAULT when an exception occurs.

    Cc: <x86@kernel.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Tony Luck <tony.luck@intel.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Co-developed-by: Tony Luck <tony.luck@intel.com>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    ---
    arch/x86/include/asm/string_64.h | 8 +++++---
    arch/x86/lib/memcpy_64.S | 20 ++++++++++++++------
    drivers/nvdimm/claim.c | 3 ++-
    drivers/nvdimm/pmem.c | 6 +++---
    include/linux/string.h | 4 ++--
    5 files changed, 26 insertions(+), 15 deletions(-)

    diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
    index 4752f8984923..d33f92b9fa22 100644
    --- a/arch/x86/include/asm/string_64.h
    +++ b/arch/x86/include/asm/string_64.h
    @@ -116,7 +116,8 @@ int strcmp(const char *cs, const char *ct);
    #endif

    #define __HAVE_ARCH_MEMCPY_MCSAFE 1
    -__must_check int __memcpy_mcsafe(void *dst, const void *src, size_t cnt);
    +__must_check unsigned long __memcpy_mcsafe(void *dst, const void *src,
    + size_t cnt);
    DECLARE_STATIC_KEY_FALSE(mcsafe_key);

    /**
    @@ -131,9 +132,10 @@ DECLARE_STATIC_KEY_FALSE(mcsafe_key);
    * actually do machine check recovery. Everyone else can just
    * use memcpy().
    *
    - * Return 0 for success, -EFAULT for fail
    + * Return 0 for success, or number of bytes not copied if there was an
    + * exception.
    */
    -static __always_inline __must_check int
    +static __always_inline __must_check unsigned long
    memcpy_mcsafe(void *dst, const void *src, size_t cnt)
    {
    #ifdef CONFIG_X86_MCE
    diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
    index 5709f3ec22a4..f01a88391c98 100644
    --- a/arch/x86/lib/memcpy_64.S
    +++ b/arch/x86/lib/memcpy_64.S
    @@ -252,14 +252,22 @@ ENDPROC(__memcpy_mcsafe)
    EXPORT_SYMBOL_GPL(__memcpy_mcsafe)

    .section .fixup, "ax"
    - /* Return -EFAULT for any failure */
    -.L_memcpy_mcsafe_fail:
    - mov $-EFAULT, %rax
    + /*
    + * Return number of bytes not copied for any failure. Note that
    + * there is no "tail" handling since the source buffer is 8-byte
    + * aligned and poison is cacheline aligned.
    + */
    +.E_read_words:
    + shll $3, %ecx
    +.E_leading_bytes:
    + addl %edx, %ecx
    +.E_trailing_bytes:
    + mov %ecx, %eax
    ret

    .previous

    - _ASM_EXTABLE_FAULT(.L_read_leading_bytes, .L_memcpy_mcsafe_fail)
    - _ASM_EXTABLE_FAULT(.L_read_words, .L_memcpy_mcsafe_fail)
    - _ASM_EXTABLE_FAULT(.L_read_trailing_bytes, .L_memcpy_mcsafe_fail)
    + _ASM_EXTABLE_FAULT(.L_read_leading_bytes, .E_leading_bytes)
    + _ASM_EXTABLE_FAULT(.L_read_words, .E_read_words)
    + _ASM_EXTABLE_FAULT(.L_read_trailing_bytes, .E_trailing_bytes)
    #endif
    diff --git a/drivers/nvdimm/claim.c b/drivers/nvdimm/claim.c
    index 30852270484f..2e96b34bc936 100644
    --- a/drivers/nvdimm/claim.c
    +++ b/drivers/nvdimm/claim.c
    @@ -276,7 +276,8 @@ static int nsio_rw_bytes(struct nd_namespace_common *ndns,
    if (rw == READ) {
    if (unlikely(is_bad_pmem(&nsio->bb, sector, sz_align)))
    return -EIO;
    - return memcpy_mcsafe(buf, nsio->addr + offset, size);
    + if (memcpy_mcsafe(buf, nsio->addr + offset, size) != 0)
    + return -EIO;
    }

    if (unlikely(is_bad_pmem(&nsio->bb, sector, sz_align))) {
    diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
    index 9d714926ecf5..e023d6aa22b5 100644
    --- a/drivers/nvdimm/pmem.c
    +++ b/drivers/nvdimm/pmem.c
    @@ -101,15 +101,15 @@ static blk_status_t read_pmem(struct page *page, unsigned int off,
    void *pmem_addr, unsigned int len)
    {
    unsigned int chunk;
    - int rc;
    + unsigned long rem;
    void *mem;

    while (len) {
    mem = kmap_atomic(page);
    chunk = min_t(unsigned int, len, PAGE_SIZE);
    - rc = memcpy_mcsafe(mem + off, pmem_addr, chunk);
    + rem = memcpy_mcsafe(mem + off, pmem_addr, chunk);
    kunmap_atomic(mem);
    - if (rc)
    + if (rem)
    return BLK_STS_IOERR;
    len -= chunk;
    off = 0;
    diff --git a/include/linux/string.h b/include/linux/string.h
    index dd39a690c841..4a5a0eb7df51 100644
    --- a/include/linux/string.h
    +++ b/include/linux/string.h
    @@ -147,8 +147,8 @@ extern int memcmp(const void *,const void *,__kernel_size_t);
    extern void * memchr(const void *,int,__kernel_size_t);
    #endif
    #ifndef __HAVE_ARCH_MEMCPY_MCSAFE
    -static inline __must_check int memcpy_mcsafe(void *dst, const void *src,
    - size_t cnt)
    +static inline __must_check unsigned long memcpy_mcsafe(void *dst,
    + const void *src, size_t cnt)
    {
    memcpy(dst, src, cnt);
    return 0;
    \
     
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      Last update: 2018-05-04 02:18    [W:4.625 / U:0.224 seconds]
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