On 06/07/2016 14:44, Borislav Petkov wrote:
> Hi guys,
>
> how about this below to enable RDTSCP emulation on AMD? IOW, I'm staring
> at
>
> 33b5e8c03ae7 ("target-i386: Disable rdtscp on Opteron_G* CPU models")
>
> in the qemu repo.
>
> It seems to work here, RDTSCP in the guest gives me node and cpu as
> vsyscall_set_cpu() in the guest kernel has set them.
>
> Thoughts?
>
> (Below is the simple qemu diff reenabling RDTSCP)
>
> @@ -3919,6 +3935,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm
> *svm) = {
> [SVM_EXIT_STGI] = stgi_interception,
> [SVM_EXIT_CLGI] = clgi_interception,
> [SVM_EXIT_SKINIT] = skinit_interception,
> + [SVM_EXIT_RDTSCP] = rdtscp_interception,
> [SVM_EXIT_WBINVD] = wbinvd_interception,
> [SVM_EXIT_MONITOR] = monitor_interception,
> [SVM_EXIT_MWAIT] = mwait_interception,
Nothing is needed in the kernel actually. You can skip the intercept
by running the guest with MSR_TSC_AUX set to the guest's expected value.
Which KVM does, except that it's botched so I need to apply the
patch in https://lkml.org/lkml/2016/4/13/802.
> ---
>
> qemu diff:
>
> ---
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 3bd3cfc3ad16..aa6d0d027d00 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
This is not enough because it's missing some backwards compatibility
gunk (similar to the include/hw/i386/pc.h parts of 33b5e8c03ae), but
it's enough for a proof of concept and to discuss it.
The main issue with this is that it would force a lockstep update of
QEMU and kernel, which we try to avoid. I'm not sure if we have a
solution for this problem. Eduardo?
Paolo
