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KVM: x86: Force TLB flush on userspace changes to special registers

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Userspace can directly modify the content of vCPU's CR0, CR3, and CR4 via
KVM_SYNC_X86_SREGS and KVM_SET_SREGS{,2}. Make sure that KVM flushes guest
TLB entries and paging-structure caches if a (partial) guest TLB flush is
architecturally required based on the CRn changes.  To keep things simple,
flush whenever KVM resets the MMU context, i.e. if any bits in CR0, CR3,
CR4, or EFER are modified.  This is extreme overkill, but stuffing state
from userspace is not such a hot path that preserving guest TLB state is a
priority.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Link: https://lore.kernel.org/r/20230814222358.707877-3-mhal@rbox.co
[sean: call out that the flushing on MMU context resets is for simplicity]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Michal Luczaj 2023-08-15 00:08:36 +02:00 committed by Sean Christopherson
parent 9dbb029b9c
commit 4346db6e6e
1 changed files with 6 additions and 2 deletions
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8
arch/x86/kvm/x86.c
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@ -11564,8 +11564,10 @@ static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
if (ret)
return ret;
if (mmu_reset_needed)
if (mmu_reset_needed) {
kvm_mmu_reset_context(vcpu);
kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
}
max_bits = KVM_NR_INTERRUPTS;
pending_vec = find_first_bit(
@ -11606,8 +11608,10 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
mmu_reset_needed = 1;
vcpu->arch.pdptrs_from_userspace = true;
}
if (mmu_reset_needed)
if (mmu_reset_needed) {
kvm_mmu_reset_context(vcpu);
kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
}
return 0;
}