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Date:   Fri, 11 Feb 2022 11:27:54 -0600
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Subject: Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when
 changing C-bit
Content-Language: en-US
To:     Borislav Petkov <bp@alien8.de>,
        "Kirill A . Shutemov" <kirill@shutemov.name>
References: <20220209181039.1262882-1-brijesh.singh@amd.com>
 <20220209181039.1262882-22-brijesh.singh@amd.com> <YgZ427v95xcdOKSC@zn.tnic>
From:   Brijesh Singh <brijesh.singh@amd.com>
In-Reply-To: <YgZ427v95xcdOKSC@zn.tnic>
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On 2/11/22 8:55 AM, Borislav Petkov wrote:
>
> Simply have them always present. They will have !0 values on the
> respective guest types and 0 otherwise. This should simplify a lot of
> code and another unconditionally present u64 won't be the end of the
> world.
>
> Any other aspect I'm missing?

I think that's mostly about it. IIUC, the recommendation is to define a
new callback in x86_platform_op. The callback will be invoked
unconditionally; The default implementation for this callback is NOP;
The TDX and SEV will override with the platform specific implementation.
I think we may able to handle everything in one callback hook but having
pre and post will be a more desirable. Here is why I am thinking so:

* On SNP, the page must be invalidated before clearing the _PAGE_ENC
from the page table attribute

* On SNP, the page must be validated after setting the _PAGE_ENC in the
page table attribute.

~Brijesh