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Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-bel
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option |
Date: |
Mon, 11 Jan 2016 13:16:39 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 |
On 01/11/16 09:26, Gerd Hoffmann wrote:
> On Fr, 2016-01-08 at 19:32 +0100, Laszlo Ersek wrote:
>> On 01/08/16 18:45, Igor Mammedov wrote:
>>> On Fri, 8 Jan 2016 13:58:03 +0100
>>> Gerd Hoffmann <address@hidden> wrote:
>>>
>>>> This patch extends the functionality of the max-ram-below-4g option
>>>> to also allow increasing lowmem. Use case: Give as much memory as
>>>> possible to legacy non-PAE guests.
>>>>
>>>> While being at it also rework the lowmem calculation logic and add a
>>>> longish comment describing how it works and what the compatibility
>>>> constrains are.
>>> CCing Laszlo as it might affect OVMF
>>
>> Thanks a lot for the CC, Igor!
>>
>> So I have to investigate this separately for i440fx and Q35.
>>
>> (1) For i440fx, OVMF determines the base of the 32-bit PCI hole like this:
>>
>> PciBase = (TopOfLowRam < BASE_2GB) ? BASE_2GB : TopOfLowRam;
>>
>> where TopOfLowRam is calculated from the CMOS registers 0x34 and 0x35.
>>
>> *If* QEMU is still sticking with the idea of git commit ddaaefb4dd, that
>> is, the 32-bit PCI hole still starts immediately after the end of low
>> RAM, then this change should be fine for i440fx.
>
> Good.
>
>> Gerd, can you confirm that this new logic for the lowmem/highmem split
>> doesn't affect the above?
>>
>> In other words, as long as there is no "void" left between the top of
>> low RAM and the base of the PCI hole, it doesn't matter where exactly
>> the split is.
>
> Yes, the logic is the same as before. Anything above ram is pci i/o.
>
>> (2) For Q35, the OVMF code is different:
>
> The patch doesn't change q35 behavior.
Thanks for confirming!
Acked-by: Laszlo Ersek <address@hidden>
- [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Gerd Hoffmann, 2016/01/08
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Marcel Apfelbaum, 2016/01/11
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Eric Blake, 2016/01/14
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Eduardo Habkost, 2016/01/19
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Gerd Hoffmann, 2016/01/20
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Eduardo Habkost, 2016/01/20
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Eduardo Habkost, 2016/01/20
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Michael S. Tsirkin, 2016/01/20
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Gerd Hoffmann, 2016/01/21
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Michael S. Tsirkin, 2016/01/21
- Re: [Qemu-devel] [PATCH v2] pc: allow raising low memory via max-ram-below-4g option, Gerd Hoffmann, 2016/01/22