Re: [RFC PATCH 09/21] KVM: TDX: Enable 2MB mapping size after TD is RUNNABLE

[Sean Christopherson <seanjc@google.com>]

On Wed, Jun 18, 2025, Kirill Shutemov wrote:
> On Wed, Jun 18, 2025 at 04:22:59AM +0300, Edgecombe, Rick P wrote:
> > On Tue, 2025-06-17 at 08:52 +0800, Yan Zhao wrote:
> > > > hopefully is just handling accepting a whole range that is not 2MB aligned.
> > > > But
> > > > I think we need to verify this more.
> > > Ok.
> > 
> > In Linux guest if a memory region is not 2MB aligned the guest will accept the

What is a "memory region" in this context?  An e820 region?  Something else?

> > ends at 4k size. If a memory region is identical to a memslot range this will be
> > fine. KVM will map the ends at 4k because it won't let huge pages span a
> > memslot. But if several memory regions are not 2MB aligned and are covered by
> > one large memslot, the accept will fail on the 4k ends under this proposal. I
> > don't know if this is a common configuration, but to cover it in the TDX guest
> > may not be trivial.
> > 
> > So I think this will only work if guests can reasonably "merge" all of the
> > adjacent accepts. Or of we declare a bunch of memory/memslot layouts illegal.
> > 
> > Kirill, how difficult would it be for TDX Linux guest to merge all 2MB adjacent
> > accepts?
> 
> Hm. What do you mean by merging?
> 
> Kernel only accepts <4k during early boot -- in EFI stub. The bitmap we
> use to track unaccepted memory tracks the status in 2M granularity and
> all later accept requests will be issues on 2M pages with fallback to 4k.
> 
> -- 
>   Kiryl Shutsemau / Kirill A. Shutemov