# Re: \[PATCH Part1 RFC v4 15/36\] x86/mm: Add support to validate memory when changing C-bit

- From: Borislav Petkov \<bp@alien8.de\>
- Date: 2021-08-17 20:44:19 
- List: linux-coco
- Page: https://ratatoskr.run/linux-coco/2021/08/1480901
- Thread: https://ratatoskr.run/kvm/2021/07/1435794/t.md

```text
On Tue, Aug 17, 2021 at 03:34:41PM -0500, Brijesh Singh wrote:
> I am not seeing any strong reason to sanity check the reserved bit in the
> psc_entry. The fields in the psc_entry are input from guest to the
> hypervisor. The hypervisor cannot trick a guest by changing anything in the
> psc_entry because guest does not read the hypervisor filled value. I am okay
> with the psc_hdr because we need to read the current and end entry after the
> PSC completes to determine whether it was successful and sanity checking PSC
> header makes much more sense. Let me know if you are okay with it ?

Ok, fair enough.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette
```