From: Joao Martins <joao.m.martins@oracle.com>
To: mlevitsk@redhat.com, Jim Mattson <jmattson@google.com>
Cc: kvm@vger.kernel.org, Will Deacon <will@kernel.org>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Thomas Gleixner <tglx@linutronix.de>,
Paolo Bonzini <pbonzini@redhat.com>,
x86@kernel.org, Robin Murphy <robin.murphy@arm.com>,
iommu@lists.linux.dev, Ingo Molnar <mingo@redhat.com>,
Joerg Roedel <joro@8bytes.org>,
Sean Christopherson <seanjc@google.com>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH 0/5] AVIC bugfixes and workarounds
Date: Tue, 26 Mar 2024 16:52:33 +0000 [thread overview]
Message-ID: <8aca78fa-1aac-4f3d-a153-284170fc0b6b@oracle.com> (raw)
In-Reply-To: <22be7d6156e38dfba1a055cc3e9cc3d10de75dbb.camel@redhat.com>
On 26/03/2024 15:59, mlevitsk@redhat.com wrote:
> On Mon, 2024-03-25 at 20:15 -0700, Jim Mattson wrote:
>>> On Thu, Sep 28, 2023 at 8:05 AM Maxim Levitsky <mlevitsk@redhat.com> wrote:
>>>>>
>>>>> Hi!
>>>>>
>>>>> This patch series includes several fixes to AVIC I found while working
>>>>> on a new version of nested AVIC code.
>>>>>
>>>>> Also while developing it I realized that a very simple workaround for
>>>>> AVIC's errata #1235 exists and included it in this patch series as well.
>>>>>
>>>>> Best regards,
>>>>> Maxim Levitsky
>>>
>>> Can someone explain why we're still unwilling to enable AVIC by
>>> default? Have the performance issues that plagued the Rome
>>> implementation been fixed? What is AMD's guidance?
>>>
> Hi
>
> This is what I know:
>
> Zen1:
> I never tested it, so I don't know how well AVIC works there and if it has any erratas.
>
> Zen2:
> Has CPU errata in regard to IPI virtualization that makes it unusable in production,
> but if AVIC's IPI virtualization (borrowing the Intel term here) is disabled,
> then it works just fine and 1:1 equivalent to APICv without IPI.
>
> I posted patches for this several times, latest version is here, it still applies I think:
> https://lkml.iu.edu/hypermail/linux/kernel/2310.0/00790.html
>
> Zen3:
> For some reason AVIC got disabled by AMD in CPUID. It is still there though and force_avic=1 kvm_amd option
> can make KVM use it and AFAIK it works just fine.
>
> It is possible that it got disabled due to Zen2 errata that is fixed on Zen3,
> but maybe AMD wasn't sure back then that it will be fixed or it might be due to performance issues with broadcast
> IPIs which I think ended up being a software issue and was fixed a long time ago.
>
> Zen4+
> I haven't tested it much, but AFAIK it should work out of the box. It also got x2avic mode which allows
> to use AVIC with VMs that have more that 254 vCPUs.
>
> IMHO if we merge the workaround I have for IPI virtualization and make IPI virtualization off for Zen2
> (and maybe Zen1 as well), then I don't see why we can't make AVIC be the default on.
Additionally, I think right now with avic=1 it fails vcpu creation when creating
more a vcpu with an id bigger than what's supported i.e. the MAX_VCPUS we
currently advertised in UAPI isn't quite honored. So that's the only wrinkle at
least I am aware. Sean had send this one series to inhibit AVIC when such config:
https://lore.kernel.org/linux-iommu/20230815213533.548732-1-seanjc@google.com/#r
But I am not sure if it was respinned.
Joao
prev parent reply other threads:[~2024-03-26 16:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-28 15:04 Maxim Levitsky
2023-09-28 15:04 ` [PATCH 1/5] x86: KVM: SVM: fix for x2avic CVE-2023-5090 Maxim Levitsky
2023-09-28 15:53 ` Sean Christopherson
2023-09-28 15:04 ` [PATCH 2/5] x86: KVM: SVM: add support for Invalid IPI Vector interception Maxim Levitsky
2023-09-28 15:46 ` Sean Christopherson
2023-09-28 15:04 ` [PATCH 3/5] x86: KVM: SVM: refresh AVIC inhibition in svm_leave_nested() Maxim Levitsky
2023-09-28 16:03 ` Sean Christopherson
2023-09-28 15:04 ` [PATCH 4/5] iommu/amd: skip updating the IRTE entry when is_run is already false Maxim Levitsky
2023-09-28 17:27 ` Joao Martins
2023-09-28 15:04 ` [PATCH 5/5] x86: KVM: SVM: workaround for AVIC's errata #1235 Maxim Levitsky
2023-09-28 15:37 ` Sean Christopherson
2024-03-26 3:15 ` [PATCH 0/5] AVIC bugfixes and workarounds Jim Mattson
2024-03-26 15:59 ` mlevitsk
2024-03-26 16:52 ` Joao Martins [this message]
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