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

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Date:   Fri, 4 Sep 2020 09:29:05 +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,

> Unless I'm mistaken, microvm doesn't even support PCI, does it?

Correct, no pci support right now.

We could probably wire up ecam (arm/virt style) for pcie support, once
the acpi support for mictovm finally landed (we need acpi for that
because otherwise the kernel wouldn't find the pcie bus).

Question is whenever there is a good reason to do so.  Why would someone
prefer microvm with pcie support over q35?

> If all of the above is true, this can be handled by adding "pci=lastbus=0"
> as a guest kernel param to override its scanning of buses.  And couldn't
> that be done by QEMU's microvm_fix_kernel_cmdline() to make it transparent
> to the end user?

microvm_fix_kernel_cmdline() is a hack, not a solution.

Beside that I doubt this has much of an effect on microvm because
it doesn't support pcie in the first place.

take care,
  Gerd