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Date:   Thu, 3 Nov 2022 00:14:04 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Michael Roth <michael.roth@amd.com>
Cc:     Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
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        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
        Hugh Dickins <hughd@google.com>,
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        "Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
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Subject: Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to
 create restricted user memory
Message-ID: <20221102211404.l5whyif3j3k67fv2@box.shutemov.name>
References: <20221025151344.3784230-1-chao.p.peng@linux.intel.com>
 <20221025151344.3784230-2-chao.p.peng@linux.intel.com>
 <20221031174738.fklhlia5fmaiinpe@amd.com>
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On Mon, Oct 31, 2022 at 12:47:38PM -0500, Michael Roth wrote:
> 
> In v8 there was some discussion about potentially passing the page/folio
> and order as part of the invalidation callback, I ended up needing
> something similar for SEV-SNP, and think it might make sense for other
> platforms. This main reasoning is:
> 
>   1) restoring kernel directmap:
> 
>      Currently SNP (and I believe TDX) need to either split or remove kernel
>      direct mappings for restricted PFNs, since there is no guarantee that
>      other PFNs within a 2MB range won't be used for non-restricted
>      (which will cause an RMP #PF in the case of SNP since the 2MB
>      mapping overlaps with guest-owned pages)

That's news to me. Where the restriction for SNP comes from? There's no
such limitation on TDX side AFAIK?

Could you point me to relevant documentation if there's any?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov