Hello David Edmondson and Igor Memmedov,
Thank you for the feedback!
For some reason I did not get your comments in my email.
I could only notice them when I opened Patchwork to get the link.
Sorry for the delay. I will do my best to address them in a few minutes.
Best regards,
Leo
On Sat, Jan 29, 2022 at 6:47 AM Leonardo Bras <leob...@redhat.com> wrote:
>
> The following steps describe a migration bug:
> 1 - Bring up a VM with -cpu EPYC on a host with EPYC-Milan cpu
> 2 - Migrate to a host with EPYC-Naples cpu
>
> The guest kernel crashes shortly after the migration.
>
> The crash happens due to a fault caused by XRSTOR:
> A set bit in XSTATE_BV is not set in XCR0.
> The faulting bit is FEATURE_PKRU (enabled in Milan, but not in Naples)
>
> To avoid this kind of bug:
> In kvm_get_xsave, mask-out from xstate_bv any bits that are not set in
> current vcpu's features.
>
> This keeps cpu->env->xstate_bv with feature bits compatible with any
> host machine capable of running the vcpu model.
>
> Signed-off-by: Leonardo Bras <leob...@redhat.com>
> ---
> target/i386/xsave_helper.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/i386/xsave_helper.c b/target/i386/xsave_helper.c
> index ac61a96344..0628226234 100644
> --- a/target/i386/xsave_helper.c
> +++ b/target/i386/xsave_helper.c
> @@ -167,7 +167,7 @@ void x86_cpu_xrstor_all_areas(X86CPU *cpu, const void
> *buf, uint32_t buflen)
> env->xmm_regs[i].ZMM_Q(1) = ldq_p(xmm + 8);
> }
>
> - env->xstate_bv = header->xstate_bv;
> + env->xstate_bv = header->xstate_bv & env->features[FEAT_XSAVE_COMP_LO];
>
> e = &x86_ext_save_areas[XSTATE_YMM_BIT];
> if (e->size && e->offset) {
> --
> 2.34.1
>
