From 60d1adfa18793f4ddb70c8e901562d8d3e9be3dc Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Thu, 30 Jun 2022 18:34:49 +0200 Subject: [PATCH] x86/ept: fix shattering of special pages MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The current logic in epte_get_entry_emt() will split any page marked as special with order greater than zero, without checking whether the super page is all special. Fix this by only splitting the page only if it's not all marked as special, in order to prevent unneeded super page shuttering. The unconditional special super page shattering has caused a performance regression on some XenServer GPU pass through workloads. Signed-off-by: Roger Pau Monné Reviewed-by: Jan Beulich Reviewed-by: Kevin Tian --- xen/arch/x86/mm/p2m-ept.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c index b04ca6dbe8..b4919bad51 100644 --- a/xen/arch/x86/mm/p2m-ept.c +++ b/xen/arch/x86/mm/p2m-ept.c @@ -491,7 +491,7 @@ int epte_get_entry_emt(struct domain *d, gfn_t gfn, mfn_t mfn, { int gmtrr_mtype, hmtrr_mtype; struct vcpu *v = current; - unsigned long i; + unsigned long i, special_pgs; *ipat = false; @@ -525,15 +525,17 @@ int epte_get_entry_emt(struct domain *d, gfn_t gfn, mfn_t mfn, return MTRR_TYPE_WRBACK; } - for ( i = 0; i < (1ul << order); i++ ) - { + for ( special_pgs = i = 0; i < (1ul << order); i++ ) if ( is_special_page(mfn_to_page(mfn_add(mfn, i))) ) - { - if ( order ) - return -1; - *ipat = true; - return MTRR_TYPE_WRBACK; - } + special_pgs++; + + if ( special_pgs ) + { + if ( special_pgs != (1ul << order) ) + return -1; + + *ipat = true; + return MTRR_TYPE_WRBACK; } switch ( type ) -- 2.30.2