Re: [PATCH v7 17/20] x86/virt/tdx: Configure global KeyID on all packages

[kirill.shutemov@xxxxxxxxxxxxxxx]

On Wed, Nov 30, 2022 at 08:34:46AM +0000, Huang, Kai wrote:
> On Wed, 2022-11-30 at 11:35 +0800, Binbin Wu wrote:
> > On 11/21/2022 8:26 AM, Kai Huang wrote:
> > > After the array of TDMRs and the global KeyID are configured to the TDX
> > > module, use TDH.SYS.KEY.CONFIG to configure the key of the global KeyID
> > > on all packages.
> > > 
> > > TDH.SYS.KEY.CONFIG must be done on one (any) cpu for each package.  And
> > > it cannot run concurrently on different CPUs.  Implement a helper to
> > > run SEAMCALL on one cpu for each package one by one, and use it to
> > > configure the global KeyID on all packages.
> > > 
> > > Intel hardware doesn't guarantee cache coherency across different
> > > KeyIDs.  The kernel needs to flush PAMT's dirty cachelines (associated
> > > with KeyID 0) before the TDX module uses the global KeyID to access the
> > > PAMT.  Following the TDX module specification, flush cache before
> > > configuring the global KeyID on all packages.
> > > 
> > > Given the PAMT size can be large (~1/256th of system RAM), just use
> > > WBINVD on all CPUs to flush.
> > > 
> > > Note if any TDH.SYS.KEY.CONFIG fails, the TDX module may already have
> > > used the global KeyID to write any PAMT.  Therefore, need to use WBINVD
> > > to flush cache before freeing the PAMTs back to the kernel.  Note using
> > > MOVDIR64B (which changes the page's associated KeyID from the old TDX
> > > private KeyID back to KeyID 0, which is used by the kernel)
> > 
> > It seems not accurate to say MOVDIR64B changes the page's associated KeyID.
> > It just uses the current KeyID for memory operations.
> 
> The "write" to the memory changes the page's associated KeyID to the KeyID that
> does the "write".  A more accurate expression perhaps should be MOVDIR64B +
> MFENSE, but I think it doesn't matter in changelog.

MOVDIR64B KeyID for the cache line, not the page. Integrity tracked on
per-cacheline basis.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov