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!" (?)
I'll send out a v3 that leaves the storage for MSR_STAR in i386 builds
and clearly documents the reason for it.
