From ffc92cf3db62443c626469ef160f9276f296f6c6 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Wed, 24 Jan 2024 15:06:50 +0200 Subject: x86/pat: Simplify the PAT programming protocol The programming protocol for the PAT MSR follows the MTRR programming protocol. However, this protocol is cumbersome and requires disabling caching (CR0.CD=1), which is not possible on some platforms. Specifically, a TDX guest is not allowed to set CR0.CD. It triggers a #VE exception. It turns out that the requirement to follow the MTRR programming protocol for PAT programming is unnecessarily strict. The new Intel Software Developer Manual (http://www.intel.com/sdm) (December 2023) relaxes this requirement, please refer to the section titled "Programming the PAT" for more information. In short, this section provides an alternative PAT update sequence which doesn't need to disable caches around the PAT update but only to flush those caches and TLBs. The AMD documentation does not link PAT programming to MTRR and is there fore, fine too. The kernel only needs to flush the TLB after updating the PAT MSR. The set_memory code already takes care of flushing the TLB and cache when changing the memory type of a page. [ bp: Expand commit message. ] Signed-off-by: Kirill A. Shutemov Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Juergen Gross Link: https://lore.kernel.org/r/20240124130650.496056-1-kirill.shutemov@linux.intel.com --- arch/x86/mm/pat/memtype.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) (limited to 'arch/x86/mm') diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index 0904d7e8e126..0d72183b5dd0 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -240,6 +240,8 @@ void pat_cpu_init(void) } wrmsrl(MSR_IA32_CR_PAT, pat_msr_val); + + __flush_tlb_all(); } /** @@ -296,13 +298,8 @@ void __init pat_bp_init(void) /* * Xen PV doesn't allow to set PAT MSR, but all cache modes are * supported. - * When running as TDX guest setting the PAT MSR won't work either - * due to the requirement to set CR0.CD when doing so. Rely on - * firmware to have set the PAT MSR correctly. */ - if (pat_disabled || - cpu_feature_enabled(X86_FEATURE_XENPV) || - cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) { + if (pat_disabled || cpu_feature_enabled(X86_FEATURE_XENPV)) { init_cache_modes(pat_msr_val); return; } -- cgit v1.2.3