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Date:   Tue, 24 Aug 2021 18:42:43 +0200
From:   Joerg Roedel <jroedel@suse.de>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Brijesh Singh <brijesh.singh@amd.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ard Biesheuvel <ardb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dov Murik <dovmurik@linux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@ibm.com>,
        Borislav Petkov <bp@alien8.de>,
        Michael Roth <michael.roth@amd.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Andi Kleen <ak@linux.intel.com>, tony.luck@intel.com,
        marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH Part2 v5 08/45] x86/fault: Add support to handle the RMP
 fault for user address
Message-ID: <YSUhg/87jZPocLDP@suse.de>
References: <20210820155918.7518-1-brijesh.singh@amd.com>
 <20210820155918.7518-9-brijesh.singh@amd.com>
 <f6d778a0-840d-8c9c-392d-5c9ffcc0bdc6@intel.com>
 <19599ede-9fc5-25e1-dcb3-98aafd8b7e87@amd.com>
 <3f426ef8-060e-ccc9-71b9-2448f2582a30@intel.com>
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On Mon, Aug 23, 2021 at 07:50:22AM -0700, Dave Hansen wrote:
> It *has* to be done in KVM, IMNHO.
> 
> The core kernel really doesn't know much about SEV.  It *really* doesn't
> know when its memory is being exposed to a virtualization architecture
> that doesn't know how to split TLBs like every single one before it.
> 
> This essentially *must* be done at the time that the KVM code realizes
> that it's being asked to shove a non-splittable page mapping into the
> SEV hardware structures.
> 
> The only other alternative is raising a signal from the fault handler
> when the page can't be split.  That's a *LOT* nastier because it's so
> much later in the process.
> 
> It's either that, or figure out a way to split hugetlbfs (and DAX)
> mappings in a failsafe way.

Yes, I agree with that. KVM needs a check to disallow HugeTLB pages in
SEV-SNP guests, at least as a temporary workaround. When HugeTLBfs
mappings can be split into smaller pages the check can be removed.

Regards,

	Joerg