Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] x86/tdx: Mark TSC reliable | Date | Thu, 24 Aug 2023 21:31:39 +0200 |
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On Tue, Aug 08 2023 at 23:01, Kirill A. Shutemov wrote: > On Tue, Aug 08, 2023 at 10:13:05AM -0700, Dave Hansen wrote: >> On 8/8/23 09:23, Kirill A. Shutemov wrote: >> ... >> > On the other hand, other clock sources (such as HPET, ACPI timer, >> > APIC, etc.) necessitate VM exits to implement, resulting in more >> > fluctuating measurements compared to TSC. Thus, those clock sources >> > are not effective for calibrating TSC. >> >> Do we need to do anything to _those_ to mark them as slightly stinky? > > I don't know what the rules here. As far as I can see, all other clock > sources relevant for TDX guest have lower rating. I guess we are fine?
Ideally they are not enumerated in the first place, which prevents the kernel from trying.
> There's notable exception to the rating order is kvmclock which is higher > than tsc.
Which is silly aside of TDX.
> It has to be disabled, but it is not clear to me how. This topic > is related to how we are going to filter allowed devices/drivers, so I > would postpone the decision until we settle on wider filtering schema.
TDX aside it might be useful to have a mechanism to select TSC over KVM clock in general.
Thanks,
tglx
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