Re: [PATCH] x86/tdx: support VM area addresses for tdx_enc_status_changed

[Sathyanarayanan Kuppuswamy]

On 8/15/25 9:43 AM, Kiryl Shutsemau wrote:
> On Thu, Aug 14, 2025 at 10:34:02PM -0400, Shixuan Zhao wrote:
> > Currently tdx_enc_status_changed uses __pa which will only accept
> > addresses within the linear mapping. This patch allows memory allocated
> > in the VM area to be used.
> >
> > For VM area addresses, we do it page-by-page since there's no guarantee
> > that the physical pages are contiguous. If, however, the entire range
> > falls within the linear mapping, we provide a fast path that do the
> > entire range just like the current version so that the performance
> > would remain roughly the same as current.
> >
> > Signed-off-by: Shixuan Zhao <shixuan.zhao@xxxxxxxxxxx>
> > ---
> > Hi,
> >
> > I recently ran into a problem where tdx_enc_status_changed was not
> > implemented to handle memory mapped in the kernel VM area (e.g., ioremap
> > or vmalloc). I have created a patch that tries to fix this problem. The
> > overall idea is to keep a fast path for the current __pa-based routine
> > if the range falls within the linear mapping, otherwise fall to a page-by-
> > page page table walk for those in the VM area.
> Could you tell more about use-case?
>
> I am not sure we ever want to convert vmalloc()ed memory to shared as it
> will result in fracturing direct mapping.
>
> And it seems to the wrong layer to make it. If we really need to go
> this pass (I am not convinced) it has to be done in set_memory.c
>
> Sathya, I remember you did something similar for REPORT, right?

Yes, we attempted something similar for Quote buffer allocation.

https://patchew.org/linux/20220609025220.2615197-1-sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx/20220609025220.2615197-4-sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx/

Our approach was to create an alias virtual mapping for the Quote buffer to
avoid modifying direct map page attributes. However, we eventually dropped
this idea due to the complexity of keeping the alias mapping in sync, as well
as issues with load_unaligned_zeropad().

Related discussion can be found in,

https://patchew.org/linux/20220609025220.2615197-1-sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx/20220609025220.2615197-5-sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx/

>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer