Messages in this thread | | | Date | Tue, 10 Jul 2018 21:47:26 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v2 1/4] x86/split_lock: Enumerate #AC exception for split locked access feature |
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On Tue, 10 Jul 2018, Dave Hansen wrote: > On 07/10/2018 11:45 AM, Fenghua Yu wrote: > > On Wed, Jul 04, 2018 at 05:07:42PM -0300, Eduardo Habkost wrote: > >> On Fri, Jun 29, 2018 at 06:23:35PM +0200, Thomas Gleixner wrote: > >>> On Fri, 29 Jun 2018, Dave Hansen wrote: > >>>> Is this MSR not really model-specific? Is it OK to go poking at it on > >>>> all x86 variants? Or, do we at _least_ need a check for Intel cpus in here? > >>> > >>> That definitely needs a vendor check. Also the whole code needs to be > >>> compiled out if CONFIG_INTEL=n. > >>> > >>> Aside of that this wants to be enumerated. CPUID or MISC_FEATURES and not > >>> this guess work detection logic. Why do I have to ask for that for every > >>> other new feature thingy? > >> > >> Yes, please. KVM hosts normally expect guests to not touch MSRs > >> unless we explicitly tell them the MSR is available (normally > >> through CPUID). This is important to ensure live migration > >> between different host kernel versions works reliably. > > > > The problem is the hardware design for the feature is complete. The > > hardware designer cannot change the feature enumeration to CPUID or > > MISC_FEATURES.
Setting a fricking bit in a CPUID leaf or in a MSR cannot be done anymore? That's just hilarious.
> Let's be honest, though. That's not *hardware* design; that is a > microcode update. We've seen what microcode updates can do _very_ > clearly with all the security issues. We (Intel) can surely fix this if > sufficiently motivated. No?
Amen to that.
And please tell your hardware people that they should stop creating features which are not enumerated in one way or the other. That's just a pain all over the place. Boot code, kernel, virt, tools ....
Thanks,
tglx
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