Re: [PATCH v7 00/42] guest_memfd: In-place conversion support

[Sean Christopherson <seanjc@google.com>]

On Wed, Jun 03, 2026, Ackerley Tng wrote:
> Ackerley Tng via B4 Relay <devnull+ackerleytng.google.com@kernel.org>
> writes:
> 
> > This is v7 of guest_memfd in-place conversion support.
> >
> 
> Here's the outstanding items after going over everyone's comments
> including Sashiko's:
> 
> + KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION
>     + Need to move page clearing into __kvm_gmem_get_pfn to resolve
>       leak where populate can put initialized kernel memory into TDX
>       guest
>     + See suggested fix at [1]

That fix works for me.  The initial guest image will typically be a tiny subset
of guest memory, so unnecessarily zeroing a few pages isn't a performance concern.

> + KVM: guest_memfd: Only prepare folios for private pages,
>     + s/non-CoCo/CoCo in commit message "INIT_SHARED is about to be
>       supported for non-CoCo VMs in a later patch in this series
>     + Use Suggested-by: Michael Roth <michael.roth@amd.com>
> + KVM: selftests: Test that shared/private status is consistent across
>   processes
>     + Improve test reliability using pthread_mutex
>     + I have a fixup patch offline.
> 	
> I would like feedback on these:
> 	
> + KVM: selftests: Test conversion with elevated page refcount
>     + Askar pointed out that soon vmsplice may not pin pages. Should I
>       pin pages through CONFIG_GUP_TEST like in [2]? I prefer not to
>       take a dependency on CONFIG_GUP_TEST.

I'm not exactly excited about taking a dependency on CONFIG_GUP_TEST either, but
it probably is the least awful choice.  E.g. KVM also pins pages is certain flows,
but we're _also_ actively working to remove the need to pin.

Hmm, maybe IORING_REGISTER_PBUF_RING?  AFAICT, it's almost literally a "pin user
memory" syscall.

> + KVM: selftests: Add script to exercise private_mem_conversions_test
>     + Would like to know what people think of a wrapper script before
>       I address Sashiko's comments.

NAK to a wrapper script.  This sounds like a perfect fit for Vipin's selftest
runner (which I'm like 4 months overdue for reviewing, testing, and merging).
If the runner _can't_ do what you want, then I'd rather improve the runner.

[*] https://lore.kernel.org/all/20260331194202.1722082-1-vipinsh@google.com

> 
> [1] https://lore.kernel.org/all/CAEvNRgEVC=fFuKVgZYvWyZD7t_zvUZihFG8hrACjvtkD5cwugw@mail.gmail.com/
> [2] https://lore.kernel.org/all/baa8838f623102931e755cf34c86314b305af49c.1747264138.git.ackerleytng@google.com/
> 
> >
> > [...snip...]
> >