[RFC PATCH 13/24] KVM: nSVM: Parameterize svm_flush_tlb_asid() by is_guest_mode

From: Yosry Ahmed
Date: Wed Mar 26 2025 - 15:41:18 EST


svm_flush_tlb_asid() currently operates on the current VMCB. In
preparation for properly tracking TLB flushes for L1 and L2 ASIDs,
refactor it to take is_guest_mode and find the proper VMCB. All existing
callers pass is_guest_mode(vcpu) to maintain existing behavior for now.

Move the comment about only flushing the current ASID to
svm_flush_tlb_all(), where it probably should have been anyway, because
svm_flush_tlb_asid() now flushes a given ASID, not the current ASID.

Create a svm_flush_tlb_guest() wrapper to use as the flush_tlb_guest()
callback.

No functional change intended.

Signed-off-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx>
---
arch/x86/kvm/svm/svm.c | 39 +++++++++++++++++++++++++--------------
1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 865c5ce4fa473..fb6b9f88a1504 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4016,25 +4016,24 @@ static void svm_enable_nmi_window(struct kvm_vcpu *vcpu)
svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
}

-static void svm_flush_tlb_asid(struct kvm_vcpu *vcpu)
+static struct vmcb *svm_get_vmcb(struct vcpu_svm *svm, bool is_guest_mode)
+{
+ return is_guest_mode ? svm->nested.vmcb02.ptr : svm->vmcb01.ptr;
+}
+
+static void svm_flush_tlb_asid(struct kvm_vcpu *vcpu, bool is_guest_mode)
{
struct vcpu_svm *svm = to_svm(vcpu);
+ struct vmcb *vmcb = svm_get_vmcb(svm, is_guest_mode);

/*
* Unlike VMX, SVM doesn't provide a way to flush only NPT TLB entries.
* A TLB flush for the current ASID flushes both "host" and "guest" TLB
* entries, and thus is a superset of Hyper-V's fine grained flushing.
*/
- kvm_hv_vcpu_purge_flush_tlb(vcpu, is_guest_mode(vcpu));
-
- /*
- * Flush only the current ASID even if the TLB flush was invoked via
- * kvm_flush_remote_tlbs(). Although flushing remote TLBs requires all
- * ASIDs to be flushed, KVM uses a single ASID for L1 and L2, and
- * unconditionally does a TLB flush on both nested VM-Enter and nested
- * VM-Exit (via kvm_mmu_reset_context()).
- */
- vmcb_set_flush_asid(svm->vmcb);
+ kvm_hv_vcpu_purge_flush_tlb(vcpu, is_guest_mode);
+ if (vmcb)
+ vmcb_set_flush_asid(vmcb);
}

static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
@@ -4050,7 +4049,7 @@ static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
if (svm_hv_is_enlightened_tlb_enabled(vcpu) && VALID_PAGE(root_tdp))
hyperv_flush_guest_mapping(root_tdp);

- svm_flush_tlb_asid(vcpu);
+ svm_flush_tlb_asid(vcpu, is_guest_mode(vcpu));
}

static void svm_flush_tlb_all(struct kvm_vcpu *vcpu)
@@ -4065,7 +4064,14 @@ static void svm_flush_tlb_all(struct kvm_vcpu *vcpu)
if (WARN_ON_ONCE(svm_hv_is_enlightened_tlb_enabled(vcpu)))
hv_flush_remote_tlbs(vcpu->kvm);

- svm_flush_tlb_asid(vcpu);
+ /*
+ * Flush only the current ASID even if the TLB flush was invoked via
+ * kvm_flush_remote_tlbs(). Although flushing remote TLBs requires all
+ * ASIDs to be flushed, KVM uses a single ASID for L1 and L2, and
+ * unconditionally does a TLB flush on both nested VM-Enter and nested
+ * VM-Exit (via kvm_mmu_reset_context()).
+ */
+ svm_flush_tlb_asid(vcpu, is_guest_mode(vcpu));
}

static void svm_flush_tlb_gva(struct kvm_vcpu *vcpu, gva_t gva)
@@ -4075,6 +4081,11 @@ static void svm_flush_tlb_gva(struct kvm_vcpu *vcpu, gva_t gva)
invlpga(gva, svm_get_current_asid(svm));
}

+static void svm_flush_tlb_guest(struct kvm_vcpu *vcpu)
+{
+ svm_flush_tlb_asid(vcpu, is_guest_mode(vcpu));
+}
+
static inline void sync_cr8_to_lapic(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -5187,7 +5198,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.flush_tlb_all = svm_flush_tlb_all,
.flush_tlb_current = svm_flush_tlb_current,
.flush_tlb_gva = svm_flush_tlb_gva,
- .flush_tlb_guest = svm_flush_tlb_asid,
+ .flush_tlb_guest = svm_flush_tlb_guest,

.vcpu_pre_run = svm_vcpu_pre_run,
.vcpu_run = svm_vcpu_run,
--
2.49.0.395.g12beb8f557-goog