diff options
author | Sean Christopherson <seanjc@google.com> | 2021-07-13 19:33:02 +0300 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-08-02 18:01:54 +0300 |
commit | 470750b3425513b9f63f176e564e63e0e7998afc (patch) | |
tree | 51df6595514d7e255ea7e85100bd9b2071aacdaf /arch/x86/kvm/vmx | |
parent | c834fd7fc1308a0e0429d203a6c3af528cd902fa (diff) | |
download | linux-470750b3425513b9f63f176e564e63e0e7998afc.tar.xz |
KVM: nVMX: Do not clear CR3 load/store exiting bits if L1 wants 'em
Keep CR3 load/store exiting enable as needed when running L2 in order to
honor L1's desires. This fixes a largely theoretical bug where L1 could
intercept CR3 but not CR0.PG and end up not getting the desired CR3 exits
when L2 enables paging. In other words, the existing !is_paging() check
inadvertantly handles the normal case for L2 where vmx_set_cr0() is
called during VM-Enter, which is guaranteed to run with paging enabled,
and thus will never clear the bits.
Removing the !is_paging() check will also allow future consolidation and
cleanup of the related code. From a performance perspective, this is
all a nop, as the VMCS controls shadow will optimize away the VMWRITE
when the controls are in the desired state.
Add a comment explaining why CR3 is intercepted, with a big disclaimer
about not querying the old CR3. Because vmx_set_cr0() is used for flows
that are not directly tied to MOV CR3, e.g. vCPU RESET/INIT and nested
VM-Enter, it's possible that is_paging() is not synchronized with CR3
load/store exiting. This is actually guaranteed in the current code, as
KVM starts with CR3 interception disabled. Obviously that can be fixed,
but there's no good reason to play whack-a-mole, and it tends to end
poorly, e.g. descriptor table exiting for UMIP emulation attempted to be
precise in the past and ended up botching the interception toggling.
Fixes: fe3ef05c7572 ("KVM: nVMX: Prepare vmcs02 from vmcs01 and vmcs12")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-25-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/vmx')
-rw-r--r-- | arch/x86/kvm/vmx/vmx.c | 46 |
1 files changed, 37 insertions, 9 deletions
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index e4b1c24ad079..9f69ccc096a3 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -2994,10 +2994,14 @@ void ept_save_pdptrs(struct kvm_vcpu *vcpu) kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR); } +#define CR3_EXITING_BITS (CPU_BASED_CR3_LOAD_EXITING | \ + CPU_BASED_CR3_STORE_EXITING) + void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0) { struct vcpu_vmx *vmx = to_vmx(vcpu); unsigned long hw_cr0; + u32 tmp; hw_cr0 = (cr0 & ~KVM_VM_CR0_ALWAYS_OFF); if (is_unrestricted_guest(vcpu)) @@ -3024,18 +3028,42 @@ void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0) #endif if (enable_ept && !is_unrestricted_guest(vcpu)) { + /* + * Ensure KVM has an up-to-date snapshot of the guest's CR3. If + * the below code _enables_ CR3 exiting, vmx_cache_reg() will + * (correctly) stop reading vmcs.GUEST_CR3 because it thinks + * KVM's CR3 is installed. + */ if (!kvm_register_is_available(vcpu, VCPU_EXREG_CR3)) vmx_cache_reg(vcpu, VCPU_EXREG_CR3); + + /* + * When running with EPT but not unrestricted guest, KVM must + * intercept CR3 accesses when paging is _disabled_. This is + * necessary because restricted guests can't actually run with + * paging disabled, and so KVM stuffs its own CR3 in order to + * run the guest when identity mapped page tables. + * + * Do _NOT_ check the old CR0.PG, e.g. to optimize away the + * update, it may be stale with respect to CR3 interception, + * e.g. after nested VM-Enter. + * + * Lastly, honor L1's desires, i.e. intercept CR3 loads and/or + * stores to forward them to L1, even if KVM does not need to + * intercept them to preserve its identity mapped page tables. + */ if (!(cr0 & X86_CR0_PG)) { - /* From paging/starting to nonpaging */ - exec_controls_setbit(vmx, CPU_BASED_CR3_LOAD_EXITING | - CPU_BASED_CR3_STORE_EXITING); - vcpu->arch.cr0 = cr0; - vmx_set_cr4(vcpu, kvm_read_cr4(vcpu)); - } else if (!is_paging(vcpu)) { - /* From nonpaging to paging */ - exec_controls_clearbit(vmx, CPU_BASED_CR3_LOAD_EXITING | - CPU_BASED_CR3_STORE_EXITING); + exec_controls_setbit(vmx, CR3_EXITING_BITS); + } else if (!is_guest_mode(vcpu)) { + exec_controls_clearbit(vmx, CR3_EXITING_BITS); + } else { + tmp = exec_controls_get(vmx); + tmp &= ~CR3_EXITING_BITS; + tmp |= get_vmcs12(vcpu)->cpu_based_vm_exec_control & CR3_EXITING_BITS; + exec_controls_set(vmx, tmp); + } + + if (!is_paging(vcpu) != !(cr0 & X86_CR0_PG)) { vcpu->arch.cr0 = cr0; vmx_set_cr4(vcpu, kvm_read_cr4(vcpu)); } |