Messages in this thread | | | Subject | Re: [RFC v2-fix-v4 1/1] x86/tdx: Skip WBINVD instruction for TDX guest | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Tue, 8 Jun 2021 21:54:28 -0700 |
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On 6/8/21 9:40 PM, Andi Kleen wrote: > >>> KVM only turns it into a noop if there is no VT-d, because with VT-d you >>> might need it to turn mappings into uncached and vice versa. >> Wow, I found the kvm_arch_register_noncoherent_dma() stuff. That's horrifying. What's it for? e > > e.g. if you want to run a GPU it really needs some uncached memory. Same is true for other more > complex devices. > > Now modern Linux of course will be preferring CLFLUSH instead for the conversion, but there are old > versions that preferred WBINVD. > > I don't think it's a DoS, as long as you're not too picky about latencies on the host. > > -Andi >
Currently we use prot_guest_has(PR_GUEST_DISABLE_WBINVD)) check for disabling the wbinvd() usage (which can be selectively enabled for tested guests).
Is it alright to generalize it with boot_cpu_has(X86_FEATURE_HYPERVISOR) without verify it?
> >
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
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