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Subject[PATCH v2 26/32] KVM: nVMX: Selectively use TLB_FLUSH_CURRENT for nested VM-Enter/VM-Exit
Date
Flush only the current context, as opposed to all contexts, when
requesting a TLB flush to handle the scenario where a L1 does not expect
a TLB flush, but one is required because L1 and L2 shared an ASID. This
occurs if EPT is disabled (no per-EPTP tag), VPID is enabled (hardware
doesn't flush unconditionally) and vmcs02 does not have its own VPID due
to exhaustion of available VPIDs.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/kvm/vmx/nested.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 19600d4b3344..04cdf7ded1d3 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -1167,16 +1167,19 @@ static void nested_vmx_transition_tlb_flush(struct kvm_vcpu *vcpu,
*
* 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 TLB as the effective ASID is common to both
- * L1 and L2.
+ * 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 (enable_vpid &&
- (!nested_cpu_has_vpid(vmcs12) || !nested_has_guest_tlb_tag(vcpu)))
- kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+ if (enable_vpid) {
+ if (!nested_cpu_has_vpid(vmcs12))
+ kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
+ else 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)
--
2.24.1
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