From: Sean Christopherson seanjc@google.com
stable inclusion from linux-4.19.206 commit 3db3ec8f3b414fa76d3a9ae864781ebbb1709a36
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commit 112022bdb5bc372e00e6e43cb88ee38ea67b97bd upstream
Mark NX as being used for all non-nested shadow MMUs, as KVM will set the NX bit for huge SPTEs if the iTLB mutli-hit mitigation is enabled. Checking the mitigation itself is not sufficient as it can be toggled on at any time and KVM doesn't reset MMU contexts when that happens. KVM could reset the contexts, but that would require purging all SPTEs in all MMUs, for no real benefit. And, KVM already forces EFER.NX=1 when TDP is disabled (for WP=0, SMEP=1, NX=0), so technically NX is never reserved for shadow MMUs.
Fixes: b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20210622175739.3610207-3-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [sudip: use old path and adjust context] Signed-off-by: Sudip Mukherjee sudipm.mukherjee@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- arch/x86/kvm/mmu.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 70a1daea09ffb..90cdd2f3d7dae 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4557,7 +4557,16 @@ static void reset_rsvds_bits_mask_ept(struct kvm_vcpu *vcpu, void reset_shadow_zero_bits_mask(struct kvm_vcpu *vcpu, struct kvm_mmu *context) { - bool uses_nx = context->nx || context->base_role.smep_andnot_wp; + /* + * KVM uses NX when TDP is disabled to handle a variety of scenarios, + * notably for huge SPTEs if iTLB multi-hit mitigation is enabled and + * to generate correct permissions for CR0.WP=0/CR4.SMEP=1/EFER.NX=0. + * The iTLB multi-hit workaround can be toggled at any time, so assume + * NX can be used by any non-nested shadow MMU to avoid having to reset + * MMU contexts. Note, KVM forces EFER.NX=1 when TDP is disabled. + */ + bool uses_nx = context->nx || !tdp_enabled || + context->base_role.smep_andnot_wp; struct rsvd_bits_validate *shadow_zero_check; int i;