From dff593c7b6eb1cfd4591b662a880a0c9325cce40 Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Thu, 10 Mar 2016 16:51:03 +0100 Subject: [PATCH] x86: don't flush the whole cache when changing cachability Introduce the FLUSH_VA_VALID flag to flush_area_mask() and friends to say that it is safe to use CLFLUSH (i.e., the virtual address is still valid). Use this when changing the cachability of the Xen direct mappings (in response to the guest changing the cachability of its mappings). This significantly improves performance by avoiding an expensive WBINVD. This fixes a performance regression introduced by c61a6f74f80eb36ed83a82f713db3143159b9009 (x86: enforce consistent cachability of MMIO mappings), the fix for XSA-154. e.g., A set_memory_wc() call in Linux: before: 4097 us after: 47 us Signed-off-by: David Vrabel Reviewed-by: Jan Beulich --- xen/arch/x86/flushtlb.c | 3 ++- xen/arch/x86/mm.c | 5 +++++ xen/include/asm-x86/flushtlb.h | 2 ++ 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/flushtlb.c b/xen/arch/x86/flushtlb.c index 582a1e254f..ee61aab1ca 100644 --- a/xen/arch/x86/flushtlb.c +++ b/xen/arch/x86/flushtlb.c @@ -140,7 +140,8 @@ unsigned int flush_area_local(const void *va, unsigned int flags) if ( order < (BITS_PER_LONG - PAGE_SHIFT) ) sz = 1UL << (order + PAGE_SHIFT); - if ( !(flags & (FLUSH_TLB|FLUSH_TLB_GLOBAL)) && + if ( (!(flags & (FLUSH_TLB|FLUSH_TLB_GLOBAL)) || + (flags & FLUSH_VA_VALID)) && c->x86_clflush_size && c->x86_cache_size && sz && ((sz >> 10) < c->x86_cache_size) ) { diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 36c44873c2..c997b5352f 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -5641,7 +5641,12 @@ int map_pages_to_xen( flush_flags |= FLUSH_TLB_GLOBAL; \ if ( (flags & _PAGE_PRESENT) && \ (((o_) ^ flags) & PAGE_CACHE_ATTRS) ) \ + { \ flush_flags |= FLUSH_CACHE; \ + if ( virt >= DIRECTMAP_VIRT_START && \ + virt < HYPERVISOR_VIRT_END ) \ + flush_flags |= FLUSH_VA_VALID; \ + } \ } while (0) while ( nr_mfns != 0 ) diff --git a/xen/include/asm-x86/flushtlb.h b/xen/include/asm-x86/flushtlb.h index 4ea31c2c0e..2e7ed6b562 100644 --- a/xen/include/asm-x86/flushtlb.h +++ b/xen/include/asm-x86/flushtlb.h @@ -85,6 +85,8 @@ void write_cr3(unsigned long cr3); #define FLUSH_TLB_GLOBAL 0x200 /* Flush data caches */ #define FLUSH_CACHE 0x400 + /* VA for the flush has a valid mapping */ +#define FLUSH_VA_VALID 0x800 /* Flush local TLBs/caches. */ unsigned int flush_area_local(const void *va, unsigned int flags); -- 2.30.2