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instructions (x86-64-stosq and similar) can vary significantly based on the chunk-size used. $ perf bench mem memset -k 4KB -s 4GB -f x86-64-stosq # Running 'mem/memset' benchmark: # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S) # Copying 4GB bytes ... 13.748208 GB/sec $ perf bench mem memset -k 2MB -s 4GB -f x86-64-stosq # Running 'mem/memset' benchmark: # function 'x86-64-stosq' (movsq-based memset() in # arch/x86/lib/memset_64.S) # Copying 4GB bytes ... 15.067900 GB/sec $ perf bench mem memset -k 1GB -s 4GB -f x86-64-stosq # Running 'mem/memset' benchmark: # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S) # Copying 4GB bytes ... 38.104311 GB/sec (Both on AMD Milan.) With a change in chunk-size of 4KB to 1GB, we see the performance go from 13.7 GB/sec to 38.1 GB/sec. For a chunk-size of 2MB the change isn't quite as drastic but it is worth adding a clear_page() variant that can handle contiguous page-extents. Define clear_user_pages() while at it. Signed-off-by: Ankur Arora --- arch/x86/include/asm/page_64.h | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h index 17b6ae89e211..289b31a4c910 100644 --- a/arch/x86/include/asm/page_64.h +++ b/arch/x86/include/asm/page_64.h @@ -43,8 +43,11 @@ extern unsigned long __phys_addr_symbol(unsigned long); void memzero_page_aligned_unrolled(void *addr, u64 len); /** - * clear_page() - clear a page using a kernel virtual address. - * @page: address of kernel page + * clear_page() - clear a page range using a kernel virtual address. + * @addr: start address + * @npages: number of pages + * + * Assumes that (@addr, +@npages) references a kernel region. * * Switch between three implementations of page clearing based on CPU * capabilities: @@ -65,21 +68,35 @@ void memzero_page_aligned_unrolled(void *addr, u64 len); * * Does absolutely no exception handling. */ -static inline void clear_page(void *page) +static inline void clear_pages(void *addr, unsigned int npages) { - u64 len = PAGE_SIZE; + u64 len = npages * PAGE_SIZE; /* - * Clean up KMSAN metadata for the page being cleared. The assembly call - * below clobbers @page, so we perform unpoisoning before it. + * Clean up KMSAN metadata for the pages being cleared. The assembly call + * below clobbers @addr, so we perform unpoisoning before it. */ - kmsan_unpoison_memory(page, len); + kmsan_unpoison_memory(addr, len); asm volatile(ALTERNATIVE_2("call memzero_page_aligned_unrolled", "shrq $3, %%rcx; rep stosq", X86_FEATURE_REP_GOOD, "rep stosb", X86_FEATURE_ERMS) - : "+c" (len), "+D" (page), ASM_CALL_CONSTRAINT + : "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT : "a" (0) : "cc", "memory"); } +#define clear_pages clear_pages + +struct page; +static inline void clear_user_pages(void *page, unsigned long vaddr, + struct page *pg, unsigned int npages) +{ + clear_pages(page, npages); +} +#define clear_user_pages clear_user_pages + +static inline void clear_page(void *addr) +{ + clear_pages(addr, 1); +} void copy_page(void *to, void *from); KCFI_REFERENCE(copy_page); -- 2.31.1