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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id z6sm12065728wro.25.2021.10.18.00.42.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Oct 2021 00:42:13 -0700 (PDT) From: Vitaly Kuznetsov To: Maxim Levitsky , Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , Tom Lendacky , David Matlack , linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] KVM: SVM: reduce guest MAXPHYADDR by one in case C-bit is a physical bit In-Reply-To: References: <20211015150524.2030966-1-vkuznets@redhat.com> Date: Mon, 18 Oct 2021 09:42:12 +0200 Message-ID: <87bl3mye23.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Maxim Levitsky writes: > On Fri, 2021-10-15 at 15:24 +0000, Sean Christopherson wrote: >> On Fri, Oct 15, 2021, Vitaly Kuznetsov wrote: >> > Several selftests (memslot_modification_stress_test, kvm_page_table_test, >> > dirty_log_perf_test,.. ) which rely on vm_get_max_gfn() started to fail >> > since commit ef4c9f4f65462 ("KVM: selftests: Fix 32-bit truncation of >> > vm_get_max_gfn()") on AMD EPYC 7401P: >> > >> > ./tools/testing/selftests/kvm/demand_paging_test >> > Testing guest mode: PA-bits:ANY, VA-bits:48, 4K pages >> > guest physical test memory offset: 0xffffbffff000 >> >> This look a lot like the signature I remember from the original bug[1]. I assume >> you're hitting the magic HyperTransport region[2]. I thought that was fixed, but >> the hack-a-fix for selftests never got applied[3]. > > Hi Vitaly and everyone! > > You are the 3rd person to suffer from this issue :-( Sean Christopherson was first, I was second. > > I reported this, then I think we found out that it is not the HyperTransport region after all, > and I think that the whole thing lost in 'trying to get answers from AMD'. > > https://lore.kernel.org/lkml/ac72b77c-f633-923b-8019-69347db706be@redhat.com/ > > > I'll say, a hack to reduce it by 1 bit is still better that failing tests, > at least until AMD explains to us, about what is going on. > > Sorry that you had to debug this. I didn't spend too much time on this, that's the reson for 'RFC' :-) I agree we need at least a short-term solution as permanently failing tests may start masking newly introduces issues. -- Vitaly