Re: [RFC PATCH v2 04/51] KVM: guest_memfd: Introduce KVM_GMEM_CONVERT_SHARED/PRIVATE ioctls

[Xu Yilun]

On Fri, Jul 18, 2025 at 11:15:59AM -0300, Jason Gunthorpe wrote:
> On Fri, Jul 18, 2025 at 10:48:55AM +0800, Xu Yilun wrote:
> > > If by the time KVM gets the conversion request, the page is unpinned,
> > > then we're all good, right?
> > 
> > Yes, unless guest doesn't unpin the page first by mistake. Guest would
> > invoke a fw call tdg.mem.page.release to unpin the page before
> > KVM_HC_MAP_GPA_RANGE.
> 
> What does guest pinning mean?

TDX firmware provides a mode, that host can't block the S-EPT mapping
after TD accepts the mapping. Guest 'pins' the private mapping (KVM &
IOMMU).

TD should explicitly unaccept the page by tdg.mem.page.release, then
host could successfully block/unmap the S-EPT. This is necessary when
shared <-> private conversion.

When TDX Connect is enabled, this mode is enforced.

Thanks,
Yilun

> 
> Jason
>