Add clear_pages_clzero(), which uses CLZERO as the clearing primitive. CLZERO skips the memory hierarchy, so this provides a non-polluting implementation of clear_page(). Available if X86_FEATURE_CLZERO is set. CLZERO, from the AMD architecture guide (Vol 3, Rev 3.30): "Clears the cache line specified by the logical address in rAX by writing a zero to every byte in the line. The instruction uses an implied non temporal memory type, similar to a streaming store, and uses the write combining protocol to minimize cache pollution. CLZERO is weakly-ordered with respect to other instructions that operate on memory. Software should use an SFENCE or stronger to enforce memory ordering of CLZERO with respect to other store instructions. The CLZERO instruction executes at any privilege level. CLZERO performs all the segmentation and paging checks that a store of the specified cache line would perform." The use-case is similar to clear_page_movnt(), except that clear_pages_clzero() is expected to be more performant. Cc: jon.grimm@xxxxxxx Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx> --- arch/x86/include/asm/page_64.h | 1 + arch/x86/lib/clear_page_64.S | 19 +++++++++++++++++++ 2 files changed, 20 insertions(+) diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h index 3affc4ecb8da..e8d4698fda65 100644 --- a/arch/x86/include/asm/page_64.h +++ b/arch/x86/include/asm/page_64.h @@ -56,6 +56,7 @@ void clear_pages_orig(void *page, unsigned long npages); void clear_pages_rep(void *page, unsigned long npages); void clear_pages_erms(void *page, unsigned long npages); void clear_pages_movnt(void *page, unsigned long npages); +void clear_pages_clzero(void *page, unsigned long npages); #define __HAVE_ARCH_CLEAR_USER_PAGES static inline void clear_pages(void *page, unsigned int npages) diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S index 83d14f1c9f57..00203103cf77 100644 --- a/arch/x86/lib/clear_page_64.S +++ b/arch/x86/lib/clear_page_64.S @@ -79,3 +79,22 @@ SYM_FUNC_START(clear_pages_movnt) ja .Lstart RET SYM_FUNC_END(clear_pages_movnt) + +/* + * Zero a page using clzero (On AMD, with CPU_FEATURE_CLZERO.) + * + * Caller needs to issue a sfence at the end. + */ +SYM_FUNC_START(clear_pages_clzero) + movq %rdi,%rax + movq %rsi,%rcx + shlq $PAGE_SHIFT, %rcx + + .p2align 4 +.Liter: + clzero + addq $0x40, %rax + subl $0x40, %ecx + ja .Liter + RET +SYM_FUNC_END(clear_pages_clzero) -- 2.31.1
