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KVM: SVM: Explicitly require FLUSHBYASID to enable SEV support

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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>
This commit is contained in:
Sean Christopherson 2023-10-18 12:36:17 -07:00
parent 176bfc5b17
commit 770d6aa2e4
1 changed files with 5 additions and 2 deletions
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7
arch/x86/kvm/svm/sev.c
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@ -2191,10 +2191,13 @@ void __init sev_hardware_setup(void)
/*
* SEV must obviously be supported in hardware. Sanity check that the
* CPU supports decode assists, which is mandatory for SEV guests to
* support instruction emulation.
* support instruction emulation. Ditto for flushing by ASID, as SEV
* guests are bound to a single ASID, i.e. KVM can't rotate to a new
* ASID to effect a TLB flush.
*/
if (!boot_cpu_has(X86_FEATURE_SEV) ||
WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)))
WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_DECODEASSISTS)) ||
WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_FLUSHBYASID)))
goto out;
/* Retrieve SEV CPUID information */