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KVM: nVMX: Emulate guest TLB flush on nested VM-Enter with new vpid12

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Fully emulate a guest TLB flush on nested VM-Enter which changes vpid12,
i.e. L2's VPID, instead of simply doing INVVPID to flush real hardware's
TLB entries for vpid02.  From L1's perspective, changing L2's VPID is
effectively a TLB flush unless "hardware" has previously cached entries
for the new vpid12.  Because KVM tracks only a single vpid12, KVM doesn't
know if the new vpid12 has been used in the past and so must treat it as
a brand new, never been used VPID, i.e. must assume that the new vpid12
represents a TLB flush from L1's perspective.

For example, if L1 and L2 share a CR3, the first VM-Enter to L2 (with a
VPID) is effectively a TLB flush as hardware/KVM has never seen vpid12
and thus can't have cached entries in the TLB for vpid12.

Reported-by: Lai Jiangshan <jiangshanlai+lkml@gmail.com>
Fixes: 5c614b3583 ("KVM: nVMX: nested VPID emulation")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211125014944.536398-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-11-25 01:49:44 +00:00 committed by Paolo Bonzini
parent 40e5f90804
commit 712494de96
1 changed files with 17 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
arch/x86/kvm/vmx/nested.c
View File

@ -1162,29 +1162,26 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
WARN_ON(!enable_vpid);
/*
* If VPID is enabled and used by vmc12, but L2 does not have a unique
* TLB tag (ASID), i.e. EPT is disabled and KVM was unable to allocate
* a VPID for L2, flush the current context as the effective ASID is
* common to both L1 and L2.
*
* Defer the flush so that it runs after vmcs02.EPTP has been set by
* KVM_REQ_LOAD_MMU_PGD (if nested EPT is enabled) and to avoid
* redundant flushes further down the nested pipeline.
*
* If a TLB flush isn't required due to any of the above, and vpid12 is
* changing then the new "virtual" VPID (vpid12) will reuse the same
* "real" VPID (vpid02), and so needs to be flushed. There's no direct
* mapping between vpid02 and vpid12, vpid02 is per-vCPU and reused for
* all nested vCPUs. Remember, a flush on VM-Enter does not invalidate
* guest-physical mappings, so there is no need to sync the nEPT MMU.
* VPID is enabled and in use by vmcs12. If vpid12 is changing, then
* emulate a guest TLB flush as KVM does not track vpid12 history nor
* is the VPID incorporated into the MMU context. I.e. KVM must assume
* that the new vpid12 has never been used and thus represents a new
* guest ASID that cannot have entries in the TLB.
*/
if (!nested_has_guest_tlb_tag(vcpu)) {
kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
} else if (is_vmenter &&
vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
if (is_vmenter && vmcs12->virtual_processor_id != vmx->nested.last_vpid) {
vmx->nested.last_vpid = vmcs12->virtual_processor_id;
vpid_sync_context(nested_get_vpid02(vcpu));
kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
return;
}
/*
* If VPID is enabled, used by vmc12, and vpid12 is not changing but
* does not have a unique TLB tag (ASID), i.e. EPT is disabled and
* KVM was unable to allocate a VPID for L2, flush the current context
* as the effective ASID is common to both L1 and L2.
*/
if (!nested_has_guest_tlb_tag(vcpu))
kvm_make_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
}
static bool is_bitwise_subset(u64 superset, u64 subset, u64 mask)