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KVM: SVM: Allow SNP guest policy disallow running with SMT enabled

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KVM currently returns -EINVAL when it attempts to create an SNP guest if
the SMT guest policy bit is not set. However, there is no reason to check
this, as there is no specific support in KVM that is required to support
this. The SEV firmware will determine if SMT has been enabled or disabled
in the BIOS and process the policy in the proper way:

 - SMT enabled in BIOS
   - Guest policy SMT == 0 ==> SNP_LAUNCH_START fails with POLICY_FAILURE
   - Guest policy SMT == 1 ==> SNP_LAUNCH_START succeeds

 - SMT disabled in BIOS
   - Guest policy SMT == 0 ==> SNP_LAUNCH_START succeeds
   - Guest policy SMT == 1 ==> SNP_LAUNCH_START succeeds

Remove the check for the SMT policy bit from snp_launch_start() and allow
the firmware to perform the proper checking.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/71043abdd9ef23b6f98fffa9c5c6045ac3a50187.1748553480.git.thomas.lendacky@amd.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Tom Lendacky
2025-05-29 16:17:59 -05:00
committed by Sean Christopherson
parent 28224ef02b
commit 9f4701e05f
1 changed files with 1 additions and 2 deletions
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3
arch/x86/kvm/svm/sev.c
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@@ -2131,8 +2131,7 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
return -EINVAL;
/* Check for policy bits that must be set */
if (!(params.policy & SNP_POLICY_MASK_RSVD_MBO) ||
!(params.policy & SNP_POLICY_MASK_SMT))
if (!(params.policy & SNP_POLICY_MASK_RSVD_MBO))
return -EINVAL;
if (params.policy & SNP_POLICY_MASK_SINGLE_SOCKET)