On 15/01/15 14:53, Jan Beulich wrote: >>>> On 15.01.15 at 15:14, <jbeul...@suse.com> wrote: >> But I think I made a wrong assumption above regarding the >> guest size: test-amd64-i386-xl-win7-amd64 produces a 64-bit >> guest with a 32-bit tool stack, so the crucial part of all the >> tests failing is not the guest's bitness, but tool stack's. So I'll >> next look into which of the three feature flags might be off >> when inspected from a 32-bit Dom0, as I now suspect that the >> guest simply doesn't get its CPUID bits correctly set up by a >> 32-bit Dom0 (i.e. the patch might just have uncovered a latent >> bug). > And there you go: The hypervisor deliberately clears the > syscall feature flag for 32-bit PV guests on non-AMD CPUs, and > hardware appears to do so too when CPUID gets executed from > a non-64-bit CS (i.e. no matter whether you execute raw or > "Xen-ified" CPUID there, you won't see that flag set). Yet 64-bit > guests won't be bothered to check whether the flag is enabled, > as x86-64 requires the feature to be there.
As AMD had supported syscall in 32bit systems for a long time, I presume it is only Intel where the feature bit in cpuid changes depending on cs.L > > But I think even if this could be taken care of in the tool stack, > it's better to have hvm_cpuid() mimic that behavior, i.e. force > FEATURE_SYSCALL on when hvm_guest_x86_mode() == 8. This seems like the least bad of the available options, but this is going to be another level of complication for my domain cpuid changes. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
