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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jan 2026 00:38:30.8320 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: bbc3c3af-dfd0-4031-7f91-08de5eceb9fa X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF00002319.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4460 Hi Boris, On 1/28/26 1:23 PM, Borislav Petkov wrote: > On Mon, Jan 26, 2026 at 04:42:04PM -0600, Kim Phillips wrote: >> The SEV-SNP IBPB-on-Entry feature does not require a guest-side >> implementation. The feature was added in Zen5 h/w, after the first >> SNP Zen implementation, and thus was not accounted for when the >> initial set of SNP features were added to the kernel. >> >> In its abundant precaution, commit 8c29f0165405 ("x86/sev: Add SEV-SNP >> guest feature negotiation support") included SEV_STATUS' IBPB-on-Entry >> bit as a reserved bit, thereby masking guests from using the feature. >> >> Unmask the bit, to allow guests to take advantage of the feature on >> hypervisor kernel versions that support it: Amend the SEV_STATUS MSR >> SNP_RESERVED_MASK to exclude bit 23 (IbpbOnEntry). > Do not explain what the patch does. For that last paragraph, how about: "Allow guests to make use of IBPB-on-Entry when supported by the hypervisor, as the bit is now architecturally defined and safe to expose." ? >> Fixes: 8c29f0165405 ("x86/sev: Add SEV-SNP guest feature negotiation support") >> Cc: Nikunj A Dadhania >> Cc: Tom Lendacky >> CC: Borislav Petkov (AMD) >> CC: Michael Roth >> Cc: stable@kernel.org > I guess... Hopefully a bitfield will be carved out for these no-explicit-guest-implementation-required bits by hardware such that we won't need to do this again. >> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h >> index 4d3566bb1a93..9016a6b00bc7 100644 >> --- a/arch/x86/include/asm/msr-index.h >> +++ b/arch/x86/include/asm/msr-index.h >> @@ -735,7 +735,10 @@ >> #define MSR_AMD64_SNP_SMT_PROT BIT_ULL(MSR_AMD64_SNP_SMT_PROT_BIT) >> #define MSR_AMD64_SNP_SECURE_AVIC_BIT 18 >> #define MSR_AMD64_SNP_SECURE_AVIC BIT_ULL(MSR_AMD64_SNP_SECURE_AVIC_BIT) >> -#define MSR_AMD64_SNP_RESV_BIT 19 >> +#define MSR_AMD64_SNP_RESERVED_BITS19_22 GENMASK_ULL(22, 19) >> +#define MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT 23 >> +#define MSR_AMD64_SNP_IBPB_ON_ENTRY BIT_ULL(MSR_AMD64_SNP_IBPB_ON_ENTRY_BIT) > Why isn't this part of SNP_FEATURES_PRESENT? > > If this feature doesn't require guest-side support, then it is trivially > present, no? SNP_FEATURES_PRESENT is for the non-trivial variety: Its bits get set as part of the patchseries that add the explicit guest support *code*. I believe 'features' like PREVENT_HOST_IBS are similar in this regard. >> +#define MSR_AMD64_SNP_RESV_BIT 24 >> #define MSR_AMD64_SNP_RESERVED_MASK GENMASK_ULL(63, MSR_AMD64_SNP_RESV_BIT) >> #define MSR_AMD64_SAVIC_CONTROL 0xc0010138 >> #define MSR_AMD64_SAVIC_EN_BIT 0 >> -- > I guess this is a fix of sorts and I could take it in now once all review > comments have been addressed... Cool, thanks. Kim