> On 12 Nov 2018, at 19:22, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>
> On Fri, Nov 9, 2018 at 2:21 PM, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>> The SYSCALL instruction is only supported in 64-bit mode on Intel
>> CPUs. With VT-x, A legacy-mode hypervisor can't launch a long-mode
>> guest. Therefore, we can omit MSR_STAR support for i386 builds.
>>
>> Note that the elided comment has not been relevant since move_msr_up()
>> was introduced in commit a75beee6e4f5d ("KVM: VMX: Avoid saving and
>> restoring msrs on lightweight vmexit").
>
> I realize now that eliminating the storage for MSR_STAR from i386
> builds breaks syscall emulation on Intel hardware when the guest CPUID
> claims "AuthenticAMD" or "AMDisbetter!" (?)
Heh.
“AMDisbetter!” seems to be a joke that was reported from early engineering samples of AMD K5 processor.
Go figure ;)
>
> I'll send out a v3 that leaves the storage for MSR_STAR in i386 builds
> and clearly documents the reason for it.
