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Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set |
Date: |
Fri, 17 Jun 2016 11:52:39 +0200 |
On Fri, 17 Jun 2016 11:17:54 +0200
Gerd Hoffmann <address@hidden> wrote:
> On Fr, 2016-06-17 at 10:43 +0200, Paolo Bonzini wrote:
> >
> > On 17/06/2016 10:15, Dr. David Alan Gilbert wrote:
> > > Larger is a problem if the guest tries to map something to a high
> > > address that's not addressable.
> >
> > Right. It's not a problem for most emulated PCI devices (it would be a
> > problem for those that have large RAM BARs, but even our emulated video
> > cards do not have 64-bit RAM BARs, I think;
>
> qxl can be configured to have one, try "-device
> qxl-vga,vram64_size_mb=1024"
>
> > > 2) While we have maxmem settings to tell us the top of VM RAM, do
> > > we have anything that tells us the top of IO space? What happens
> > > when we hotplug a PCI card?
>
> > (arch/x86/kernel/setup.c) but I agree that (2) is a blocker.
>
> seabios maps stuff right above ram (possibly with a hole due to
> alignment requirements).
>
> ovmf maps stuff into a 32G-aligned 32G hole. Which lands at 32G and
> therefore is addressable with 36 bits, unless you have tons of ram (>
> 30G) assigned to your guest. A physical host machine where you can plug
> in enough ram for such a configuration likely has more than 36 physical
> address lines too ...
>
> qemu checks where the firmware mapped 64bit bars, then adds those ranges
> to the root bus pci resources in the acpi tables (see /proc/iomem).
>
> > You don't know how the guest will assign PCI BAR addresses, and as you
> > said there's hotplug too.
>
> Not sure whenever qemu adds some extra space for hotplug to the 64bit
> hole and if so how it calculates the size then. But the guest os should
> stick to those ranges when configuring hotplugged devices.
currently firmware would assign 64-bit BARs after reserved-memory-end
(not sure about ovmf though) but QEMU on ACPI side will add 64-bit _CRS only
for firmware mapped devices (i.e. no space reserved for hotplug).
And is I recall correctly ovmf won't map BARs if it doesn't have
a driver for it so ACPI tables won't even have a space for not mapped
64-bit BARs.
There was another attempt to reserve more space in _CRS
https://lists.nongnu.org/archive/html/qemu-devel/2016-05/msg00090.html
>
> cheers,
> Gerd
>
>
- Re: [Qemu-devel] [PATCH 3/5] x86: fill high bits of mtrr mask, (continued)
- [Qemu-devel] [PATCH 5/5] x86: Set physical address bits based on host, Dr. David Alan Gilbert (git), 2016/06/16
- [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Dr. David Alan Gilbert (git), 2016/06/16
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Paolo Bonzini, 2016/06/16
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Eduardo Habkost, 2016/06/16
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Dr. David Alan Gilbert, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Paolo Bonzini, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Gerd Hoffmann, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set,
Igor Mammedov <=
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Gerd Hoffmann, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Laszlo Ersek, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Laszlo Ersek, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Marcel Apfelbaum, 2016/06/19
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Igor Mammedov, 2016/06/20
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Marcel Apfelbaum, 2016/06/20
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Dr. David Alan Gilbert, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Paolo Bonzini, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Eduardo Habkost, 2016/06/17
- Re: [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set, Paolo Bonzini, 2016/06/17