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Commit 4f76285f authored by Sean Christopherson's avatar Sean Christopherson Committed by Greg Kroah-Hartman
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KVM: x86/mmu: Treat NX as used (not reserved) for all !TDP shadow MMUs 



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: b8e8c830 ("kvm: mmu: ITLB_MULTIHIT mitigation")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-3-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
[sudip: use old path]
Signed-off-by: default avatarSudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 620681d7

arch/x86/kvm/mmu.c

+9 −1
Original line number Diff line number Diff line
@@ -4666,7 +4666,15 @@ 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 ||

	/*

	 * 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->mmu_role.base.smep_andnot_wp;

	struct rsvd_bits_validate *shadow_zero_check;

	int i;