Re: [PATCH v2] x86: Skip WBINVD instruction for VM guest

Dave Hansen
2021-12-04T00:20:39Z

On 12/3/21 3:49 PM, Kirill A. Shutemov wrote:
> - ACPI_FLUSH_CPU_CACHE();
> + if (acpi_state >= ACPI_STATE_S1 && acpi_state <= ACPI_STATE_S3)
> + ACPI_FLUSH_CPU_CACHE();

It's a bit of a bummer that this per-sleep-state logic has to be
repeated so many time.

If you pass acpi_state into ACPI_FLUSH_CPU_CACHE() can you centralize
the set of places where that knowledge about which sleep states require
flushing?

> TDX doesn't support these S- and C-states. TDX is only supports S0 and S5.

This makes me a bit nervous. Is this "the first TDX implementation
supports..." or "the TDX architecture *prohibits* supporting S1 (or
whatever"?

I really think we need some kind of architecture guarantee. Without
that, we risk breaking things if someone at our employer simply changes
their mind.

The:

> #define ACPI_FLUSH_CPU_CACHE_PHYS() \
> if (!cpu_feature_enabled(XXX)) \
> wbinvd(); \

does seem simpler and less error-prone than this, though.