Messages in this thread | | | Date | Mon, 28 Feb 2022 19:37:13 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv4 29/30] ACPICA: Avoid cache flush on TDX guest |
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On Sun, Feb 27, 2022 at 05:34:45PM -0800, Dan Williams wrote: > On Sun, Feb 27, 2022 at 2:05 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > > > On Thu, Feb 24, 2022 at 06:56:29PM +0300, Kirill A. Shutemov wrote: > > > +/* > > > + * ACPI_FLUSH_CPU_CACHE() flushes caches on entering sleep states. > > > + * It is required to prevent data loss. > > > + * > > > + * While running inside TDX guest, the kernel can bypass cache flushing. > > > + * Changing sleep state in a virtual machine doesn't affect the host system > > > + * sleep state and cannot lead to data loss. > > > + * > > > + * TODO: Is it safe to generalize this from TDX guests to all guest kernels? > > > + */ > > > +#define ACPI_FLUSH_CPU_CACHE() \ > > > +do { \ > > > + if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) \ > > > + wbinvd(); \ > > > +} while (0) > > > > If it's safe, why not do it for all VMs? Is there something specific > > about TDX which makes this more obviously known to be safe than for > > regular VMs? > > > > The patch description and the above comment make it sound like "we're > > not really sure this is safe, so we'll just use TDX as a testing ground > > for the idea." Which doesn't really inspire a lot of confidence in the > > stability of TD sleep states. > > Agree, why is this marked as "TODO"? The cache flushes associated with > ACPI sleep states are to flush cache before bare metal power loss to > CPU caches and bare metal transition of DDR in self-refresh mode. If a > cache flush is required it is the responsibility of the hypervisor. > Either it is safe for all guests or it is unsafe for all guests, not > TD specific.
Do we have "any VM" check? I can't find it right away.
-- Kirill A. Shutemov
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