From 90b926e68f500844dff16b5bcea178dc55cf580a Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Tue, 10 Jan 2023 07:54:27 +0100 Subject: [PATCH] x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case Since 72cbc8f04fe2 ("x86/PAT: Have pat_enabled() properly reflect state when running on Xen") PAT can be enabled without MTRR. This has resulted in problems e.g. for a SEV-SNP guest running under Hyper-V, when trying to establish a new mapping via memremap() with WB caching mode, as pat_x_mtrr_type() will call mtrr_type_lookup(), which in turn is returning MTRR_TYPE_INVALID due to MTRR being disabled in this configuration. The result is a mapping with UC- caching, leading to severe performance degradation. Fix that by handling MTRR_TYPE_INVALID the same way as MTRR_TYPE_WRBACK in pat_x_mtrr_type() because MTRR_TYPE_INVALID means MTRRs are disabled. [ bp: Massage commit message. ] Fixes: 72cbc8f04fe2 ("x86/PAT: Have pat_enabled() properly reflect state when running on Xen") Reported-by: Michael Kelley (LINUX) Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Michael Kelley Tested-by: Michael Kelley Cc: Link: https://lore.kernel.org/r/20230110065427.20767-1-jgross@suse.com --- arch/x86/mm/pat/memtype.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index 46de9cf..fb4b1b5 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -387,7 +387,8 @@ static unsigned long pat_x_mtrr_type(u64 start, u64 end, u8 mtrr_type, uniform; mtrr_type = mtrr_type_lookup(start, end, &uniform); - if (mtrr_type != MTRR_TYPE_WRBACK) + if (mtrr_type != MTRR_TYPE_WRBACK && + mtrr_type != MTRR_TYPE_INVALID) return _PAGE_CACHE_MODE_UC_MINUS; return _PAGE_CACHE_MODE_WB; -- 2.7.4