linux-kernel - Re: [PATCH Part2 RFC v4 10/40] x86/fault: Add support to handle the RMP fault for user address

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Date:   Mon, 12 Jul 2021 09:29:34 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Brijesh Singh <brijesh.singh@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 10/40] x86/fault: Add support to handle the
 RMP fault for user address

On 7/12/21 9:24 AM, Brijesh Singh wrote:
> Apologies if I was not clear in the messaging, that's exactly what I
> mean that we don't feed RMP entries during the page state change.
> 
> The sequence of the operation is:
> 
> 1. Guest issues a VMGEXIT (page state change) to add a page in the RMP
> 2. Hyperivosr adds the page in the RMP table.
> 
> The check will be inside the hypervisor (#2), to query the backing page
> type, if the backing page is from the hugetlbfs, then don't add the page
> in the RMP, and fail the page state change VMGEXIT.

Right, but *LOOOOOONG* before that, something walked the page tables and
stuffed the PFN into the NPT (that's the AMD equivalent of EPT, right?).
 You could also avoid this whole mess by refusing to allow hugetblfs to
be mapped into the guest in the first place.