On Wed, Oct 13, 2021 at 9:56 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > The size of the data in the scratch buffer is not divided by the size of > each port I/O operation, so vcpu->arch.pio.count ends up being larger > than it should be by a factor of size. > > Cc: stable@xxxxxxxxxxxxxxx > Fixes: 7ed9abfe8e9f ("KVM: SVM: Support string IO operations for an SEV-ES guest") > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> > --- > arch/x86/kvm/svm/sev.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index c36b5fe4c27c..e672493b5d8d 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -2583,7 +2583,7 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in) > return -EINVAL; > > return kvm_sev_es_string_io(&svm->vcpu, size, port, > - svm->ghcb_sa, svm->ghcb_sa_len, in); > + svm->ghcb_sa, svm->ghcb_sa_len / size, in); > } > > void sev_es_init_vmcb(struct vcpu_svm *svm) > -- > 2.27.0 > > I could be missing something, but I'm pretty sure that this is wrong. The GHCB spec says that `exit_info_2` is the `rep` count. Not the string length. For example, given a `rep outsw` instruction, with `ECX` set to `8`, the rep count written into `SW_EXITINFO2` should be eight x86 words (i.e., 16 bytes) and the IO size should be one x86 word (i.e., 2 bytes). In other words, the code was correct before this patch. This patch is incorrectly dividing the rep count by the IO size, causing the string IO to be truncated.