xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

KVM: add explicit barrier to kvm_vcpu_kick

Browse Source 
kvm_vcpu_kick() must issue a general memory barrier prior to reading
vcpu->mode in order to ensure correctness of the mutual-exclusion
memory barrier pattern used with vcpu->requests.  While the cmpxchg
called from kvm_vcpu_kick():

 kvm_vcpu_kick
   kvm_arch_vcpu_should_kick
     kvm_vcpu_exiting_guest_mode
       cmpxchg

implies general memory barriers before and after the operation, that
implication is only valid when cmpxchg succeeds.  We need an explicit
barrier for when it fails, otherwise a VCPU thread on its entry path
that reads zero for vcpu->requests does not exclude the possibility
the requesting thread sees !IN_GUEST_MODE when it reads vcpu->mode.

kvm_make_all_cpus_request already had a barrier, so we remove it, as
now it would be redundant.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Andrew Jones
2017-04-26 22:32:24 +02:00
committed by Paolo Bonzini
parent 6c6e8360b3
commit cde9af6e79
3 changed files with 7 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/kvm/x86.c
View File

@@ -6853,7 +6853,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
/*
* 1) We should set ->mode before checking ->requests. Please see
* the comment in kvm_make_all_cpus_request.
* the comment in kvm_vcpu_exiting_guest_mode().
*
* 2) For APICv, we should set ->mode before checking PIR.ON. This
* pairs with the memory barrier implicit in pi_test_and_set_on