Commit a506fdd2 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
Browse files

KVM: nSVM: implement nested_svm_load_cr3() and use it for host->guest switch 



Undesired triple fault gets injected to L1 guest on SVM when L2 is
launched with certain CR3 values. #TF is raised by mmu_check_root()
check in fast_pgd_switch() and the root cause is that when
kvm_set_cr3() is called from nested_prepare_vmcb_save() with NPT
enabled CR3 points to a nGPA so we can't check it with
kvm_is_visible_gfn().

Using generic kvm_set_cr3() when switching to nested guest is not
a great idea as we'll have to distinguish between 'real' CR3s and
'nested' CR3s to e.g. not call kvm_mmu_new_pgd() with nGPA. Following
nVMX implement nested-specific nested_svm_load_cr3() doing the job.

To support the change, nested_svm_load_cr3() needs to be re-ordered
with nested_svm_init_mmu_context().

Note: the current implementation is sub-optimal as we always do TLB
flush/MMU sync but this is still an improvement as we at least stop doing
kvm_mmu_reset_context().

Fixes: 7c390d35 ("kvm: x86: Add fast CR3 switch code path")
Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200710141157.1640173-8-vkuznets@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent bf7dea42

arch/x86/kvm/mmu/mmu.c

+2 −0
Original line number Diff line number Diff line
@@ -4952,6 +4952,8 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, u32 cr0, u32 cr4, u32 efer, 
	union kvm_mmu_role new_role =

		kvm_calc_shadow_mmu_root_page_role(vcpu, false);



	__kvm_mmu_new_pgd(vcpu, nested_cr3, new_role.base, false, false);



	if (new_role.as_u64 != context->mmu_role.as_u64)

		shadow_mmu_init_context(vcpu, context, cr0, cr4, efer, new_role);

}

arch/x86/kvm/svm/nested.c

+29 −9
Original line number Diff line number Diff line
@@ -348,7 +348,28 @@ static inline bool nested_npt_enabled(struct vcpu_svm *svm) 
static int nested_svm_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3,

			       bool nested_npt)

{

	return kvm_set_cr3(vcpu, cr3);

	if (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63))

		return -EINVAL;



	if (!nested_npt && is_pae_paging(vcpu) &&

	    (cr3 != kvm_read_cr3(vcpu) || pdptrs_changed(vcpu))) {

		if (!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))

			return -EINVAL;

	}



	/*

	 * TODO: optimize unconditional TLB flush/MMU sync here and in

	 * kvm_init_shadow_npt_mmu().

	 */

	if (!nested_npt)

		kvm_mmu_new_pgd(vcpu, cr3, false, false);



	vcpu->arch.cr3 = cr3;

	kvm_register_mark_available(vcpu, VCPU_EXREG_CR3);



	kvm_init_mmu(vcpu, false);



	return 0;

}



static void nested_prepare_vmcb_save(struct vcpu_svm *svm, struct vmcb *nested_vmcb)
@@ -364,9 +385,6 @@ static void nested_prepare_vmcb_save(struct vcpu_svm *svm, struct vmcb *nested_v 
	svm_set_efer(&svm->vcpu, nested_vmcb->save.efer);

	svm_set_cr0(&svm->vcpu, nested_vmcb->save.cr0);

	svm_set_cr4(&svm->vcpu, nested_vmcb->save.cr4);

	(void)nested_svm_load_cr3(&svm->vcpu, nested_vmcb->save.cr3,

				  nested_npt_enabled(svm));



	svm->vmcb->save.cr2 = svm->vcpu.arch.cr2 = nested_vmcb->save.cr2;

	kvm_rax_write(&svm->vcpu, nested_vmcb->save.rax);

	kvm_rsp_write(&svm->vcpu, nested_vmcb->save.rsp);
@@ -388,11 +406,6 @@ static void nested_prepare_vmcb_control(struct vcpu_svm *svm) 
	if (nested_npt_enabled(svm))

		nested_svm_init_mmu_context(&svm->vcpu);



	/* Guest paging mode is active - reset mmu */

	kvm_mmu_reset_context(&svm->vcpu);



	svm_flush_tlb(&svm->vcpu);



	svm->vmcb->control.tsc_offset = svm->vcpu.arch.tsc_offset =

		svm->vcpu.arch.l1_tsc_offset + svm->nested.ctl.tsc_offset;
@@ -424,11 +437,18 @@ static void nested_prepare_vmcb_control(struct vcpu_svm *svm) 
int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,

			  struct vmcb *nested_vmcb)

{

	int ret;



	svm->nested.vmcb = vmcb_gpa;

	load_nested_vmcb_control(svm, &nested_vmcb->control);

	nested_prepare_vmcb_save(svm, nested_vmcb);

	nested_prepare_vmcb_control(svm);



	ret = nested_svm_load_cr3(&svm->vcpu, nested_vmcb->save.cr3,

				  nested_npt_enabled(svm));

	if (ret)

		return ret;



	svm_set_gif(svm, true);



	return 0;

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