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KVM: SVM: Explicitly require FLUSHBYASID to enable SEV support
Add a sanity check that FLUSHBYASID is available if SEV is supported in hardware, as SEV (and beyond) guests are bound to a single ASID, i.e. KVM can't "flush" by assigning a new, fresh ASID to the guest. If FLUSHBYASID isn't supported for some bizarre reason, KVM would completely fail to do TLB flushes for SEV+ guests (see pre_svm_run() and pre_sev_run()). Cc: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lore.kernel.org/r/20231018193617.1895752-1-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
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@ -2191,10 +2191,13 @@ void __init sev_hardware_setup(void)
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/*
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* SEV must obviously be supported in hardware. Sanity check that the
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* CPU supports decode assists, which is mandatory for SEV guests to
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* support instruction emulation.
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* support instruction emulation. Ditto for flushing by ASID, as SEV
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* guests are bound to a single ASID, i.e. KVM can't rotate to a new
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* ASID to effect a TLB flush.
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*/
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if (!boot_cpu_has(X86_FEATURE_SEV) ||
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WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)))
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WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)) ||
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WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_FLUSHBYASID)))
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goto out;
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/* Retrieve SEV CPUID information */
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