linux-kernel - Re: [PATCH v2 0/3] KVM: x86: KVM_MEM_PCI

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Message-ID: <20200918084906.ja5elzh5zli47mg3@sirius.home.kraxel.org>
Date:   Fri, 18 Sep 2020 10:49:06 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Peter Xu <peterx@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Tsirkin <mst@...hat.com>,
        Julia Suvorova <jsuvorov@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Jones <drjones@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] KVM: x86: KVM_MEM_PCI_HOLE memory

  Hi,

> I see a similar ~8k PCI hole reads with a -kernel boot w/ OVMF.  All but 60
> of those are from pcibios_fixup_peer_bridges(), and all are from the kernel.

pcibios_fixup_peer_bridges() looks at pcibios_last_bus, and that in turn
seems to be set according to the mmconfig size (in
arch/x86/pci/mmconfig-shared.c).

So, maybe we just need to declare a smaller mmconfig window in the acpi
tables, depending on the number of pci busses actually used ...

> If all of the above is true, this can be handled by adding "pci=lastbus=0"

... so we don't need manual quirks like this?

take care,
  Gerd