Messages in this thread | | | From | Dan Williams <> | Date | Tue, 8 Jun 2021 21:19:04 -0700 | Subject | Re: [RFC v2-fix-v4 1/1] x86/tdx: Skip WBINVD instruction for TDX guest |
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On Tue, Jun 8, 2021 at 8:56 PM Kuppuswamy, Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> wrote: > > > > On 6/8/21 8:40 PM, Dan Williams wrote: > > ..."KVM gets away with it" is not a justification that TDX can stand > > on otherwise we would not be here fixing up ACPICA properly. > > > > How about: > > > > "TDX guests use standard ACPI mechanisms to signal sleep state entry > > (including reboot) to the host. The ACPI specification mandates WBINVD > > on any sleep state entry with the expectation that the platform is > > only responsible for maintaining the state of memory over sleep > > states, not preserving dirty data in any CPU caches. ACPI cache > > flushing requirements pre-date the advent of virtualization. Given TDX > > guest sleep state entry does not affect any host power rails it is not > > required to flush caches. The host is responsible for maintaining > > cache state over its own bare metal sleep state transitions that > > power-off the cache. If the host fails to manage caches over its sleep > > state transitions the guest..." > > > > > I don't know how to finish the last sentence. What does TDX do if it > > is resumed after host suspend and the host somehow arranged for dirty > > TDX lines to be lost. > > TDX guest does not support S3. It will be disabled in ACPI tables. It > is a TDX firmware spec requirement. Please check the following spec, > sec 2.1 > > https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-virtual-firmware-design-guide-rev-1.pdf
I'm not asking about TDX guest entering S3...
> > In TDX guest, we encounter cache flushes only in shutdown and reboot path. > So there is no resume path.
Host is free to go into S3 independent of any guest state. A hostile host is free to do just enough cache management so that it can resume from S3 while arranging for TDX guest dirty data to be lost. Does a TDX guest go fatal if the cache loses power?
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