Messages in this thread | | | Date | Mon, 8 Jan 2018 11:08:55 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [tip:x86/pti] x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE_RDTSC |
| |
On Sat, 6 Jan 2018, tip-bot for Tom Lendacky wrote:
> Commit-ID: 0bf17c102177d5da9363bf8b1e4704b9996d5079 > Gitweb: https://git.kernel.org/tip/0bf17c102177d5da9363bf8b1e4704b9996d5079 > Author: Tom Lendacky <thomas.lendacky@amd.com> > AuthorDate: Fri, 5 Jan 2018 10:07:56 -0600 > Committer: Thomas Gleixner <tglx@linutronix.de> > CommitDate: Sat, 6 Jan 2018 21:57:40 +0100 > > x86/cpu/AMD: Use LFENCE_RDTSC instead of MFENCE_RDTSC > > With LFENCE now a serializing instruction, set the LFENCE_RDTSC > feature since the LFENCE instruction has less overhead than the > MFENCE instruction.
Second thoughts on that. As pointed out by someone in one of the insane long threads:
What happens if the kernel runs as a guest and
- the hypervisor did not set the LFENCE to serializing on the host
- the hypervisor does not allow writing MSR_AMD64_DE_CFG
That would bring the guest into a pretty bad state or am I missing something essential here?
I'm dropping these patches until this question is answered.
Thanks,
tglx
| |