linux-kernel - [PATCH RFC 0/2] KVM: x86: allow for more CPUID entries

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Message-Id: <20200915154306.724953-1-vkuznets@redhat.com>
Date:   Tue, 15 Sep 2020 17:43:04 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Wei Huang <whuang2@....com>, linux-kernel@...r.kernel.org
Subject: [PATCH RFC 0/2] KVM: x86: allow for more CPUID entries

With QEMU and newer AMD CPUs (namely: Epyc 'Rome') the current limit for
KVM_MAX_CPUID_ENTRIES(80) is reported to be hit. Last time it was raised
from '40' in 2010. We can, of course, just bump it a little bit to fix
the immediate issue but the report made me wonder why we need to pre-
allocate vcpu->arch.cpuid_entries array instead of sizing it dynamically.
This RFC is intended to feed my curiosity.

Very mildly tested with selftests/kvm-unit-tests and nothing seems to
break. I also don't have access to the system where the original issue
was reported but chances we're fixing it are very good IMO as just the
second patch alone was reported to be sufficient.

Reported-by: Dr. David Alan Gilbert <dgilbert@...hat.com>

Vitaly Kuznetsov (2):
  KVM: x86: allocate vcpu->arch.cpuid_entries dynamically
  KVM: x86: bump KVM_MAX_CPUID_ENTRIES

 arch/x86/include/asm/kvm_host.h |  4 +--
 arch/x86/kvm/cpuid.c            | 55 ++++++++++++++++++++++++---------
 arch/x86/kvm/x86.c              |  1 +
 3 files changed, 43 insertions(+), 17 deletions(-)

-- 
2.25.4