On 16/09/21 00:40, Marc Orr wrote:
On Wed, Sep 15, 2021 at 10:18 AM Peter Gonda <pgonda@xxxxxxxxxx> wrote:
Adds vcpu mutex guard to the VMSA updating code. Refactors out
__sev_launch_update_vmsa() function to deal with per vCPU parts
of sev_launch_update_vmsa().
Can you expand the changelog, and perhaps add a comment into the
source code as well, to explain what grabbing the mutex protects us
from? I assume that it's a poorly behaved user-space, rather than a
race condition in a well-behaved user-space VMM, but I'm not certain.
Other than that, the patch itself seems fine to me.
I added this:
The update-VMSA ioctl touches data stored in struct kvm_vcpu, and
therefore should not be performed concurrently with any VCPU ioctl
that might cause KVM or the processor to use the same data.
Paolo
Fixes: ad73109ae7ec ("KVM: SVM: Provide support to launch and run an SEV-ES guest")
Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx>
Cc: Marc Orr <marcorr@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
V2
* Refactor per vcpu work to separate function.
* Remove check to skip already initialized VMSAs.
* Removed vmsa struct zeroing.
---
arch/x86/kvm/svm/sev.c | 53 ++++++++++++++++++++++++------------------
1 file changed, 30 insertions(+), 23 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 75e0b21ad07c..766510fe3abb 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -595,43 +595,50 @@ static int sev_es_sync_vmsa(struct vcpu_svm *svm)
return 0;
}
-static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
+static int __sev_launch_update_vmsa(struct kvm *kvm, struct kvm_vcpu *vcpu,
+ int *error)
{
- struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
struct sev_data_launch_update_vmsa vmsa;
+ struct vcpu_svm *svm = to_svm(vcpu);
+ int ret;
+
+ /* Perform some pre-encryption checks against the VMSA */
+ ret = sev_es_sync_vmsa(svm);
+ if (ret)
+ return ret;
+
+ /*
+ * The LAUNCH_UPDATE_VMSA command will perform in-place encryption of
+ * the VMSA memory content (i.e it will write the same memory region
+ * with the guest's key), so invalidate it first.
+ */
+ clflush_cache_range(svm->vmsa, PAGE_SIZE);
+
+ vmsa.reserved = 0;
+ vmsa.handle = to_kvm_svm(kvm)->sev_info.handle;
+ vmsa.address = __sme_pa(svm->vmsa);
+ vmsa.len = PAGE_SIZE;
+ return sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_VMSA, &vmsa, error);
+}
+
+static int sev_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
struct kvm_vcpu *vcpu;
int i, ret;
if (!sev_es_guest(kvm))
return -ENOTTY;
- vmsa.reserved = 0;
-
- kvm_for_each_vcpu(i, vcpu, kvm) {
- struct vcpu_svm *svm = to_svm(vcpu);
-
- /* Perform some pre-encryption checks against the VMSA */
- ret = sev_es_sync_vmsa(svm);
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ ret = mutex_lock_killable(&vcpu->mutex);
if (ret)
return ret;
- /*
- * The LAUNCH_UPDATE_VMSA command will perform in-place
- * encryption of the VMSA memory content (i.e it will write
- * the same memory region with the guest's key), so invalidate
- * it first.
- */
- clflush_cache_range(svm->vmsa, PAGE_SIZE);
+ ret = __sev_launch_update_vmsa(kvm, vcpu, &argp->error);
- vmsa.handle = sev->handle;
- vmsa.address = __sme_pa(svm->vmsa);
- vmsa.len = PAGE_SIZE;
- ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_VMSA, &vmsa,
- &argp->error);
+ mutex_unlock(&vcpu->mutex);
if (ret)
return ret;
-
- svm->vcpu.arch.guest_state_protected = true;
}
return 0;
--
2.33.0.464.g1972c5931b-goog
