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Date: Fri, 15 Oct 2021 16:44:02 +0000 From: Sean Christopherson <seanjc@...gle.com> To: Brijesh Singh <brijesh.singh@....com> Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev, linux-mm@...ck.org, linux-crypto@...r.kernel.org, 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>, 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>, "Kirill A . Shutemov" <kirill@...temov.name>, Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com, marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com Subject: Re: [PATCH Part2 v5 34/45] KVM: SVM: Do not use long-lived GHCB map while setting scratch area On Fri, Oct 15, 2021, Brijesh Singh wrote: > > On 10/13/21 2:20 PM, Sean Christopherson wrote: > > On Fri, Aug 20, 2021, Brijesh Singh wrote: > >> The setup_vmgexit_scratch() function may rely on a long-lived GHCB > >> mapping if the GHCB shared buffer area was used for the scratch area. > >> In preparation for eliminating the long-lived GHCB mapping, always > >> allocate a buffer for the scratch area so it can be accessed without > >> the GHCB mapping. > > Would it make sense to post this patch and the next (Remove the long-lived GHCB > > host map) in a separate mini-series? It's needed for SNP, but AFAICT there's > > nothing that depends on SNP. Getting this merged ahead of time would reduce the > > size of the SNP series by a smidge. > > While testing with random configs, I am seeing some might_sleep() warns. > This is happening mainly because during the vmrun the GHCB is accessed > with preempt disabled. The kvm_vcpu_map() -> kmap() reports the warning. > I am leaning towards creating a cache on the vmgexit and use that cache > instead of the doing a kmap() on every access. Does that sound okay to you ? Since SEV is 64-bit only, it should be ok to add a kvm_vcpu_map_atomic() variant.
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