[edk2-devel] [PATCH v2 2/4] OvmfPkg/PlatformInitLib: Add PlatformGetLowMemoryCB
Laszlo Ersek
lersek at redhat.com
Thu Jan 12 15:44:56 UTC 2023
On 1/12/23 15:03, Gerd Hoffmann wrote:
> Hi,
>
>>> I think it should actually simplify things. All the inconsistencies we
>>> have (as you outlined above) due to the hole punching and edk2
>>> supporting only a single range for 32bit mmio should go away, and we
>>> will have less address space layout differences between q35 and pc.
>>
>> We've tried 0xE000_0000 in the past, in commit 75136b29541b.
>>
>> But had to revert it in commit eb4d62b0779c, due to 0xE000_0000 tickling
>> a bug in QEMU.
>>
>> The bug tickling was actually reported by you :) See
>> <https://bugzilla.tianocore.org/show_bug.cgi?id=1859>.
>
> Oh. I totally forgot about that. The patch from (I think) 2019 which
> added _CRS for the range below the MMCONFIG should have fixed that, and
> with recent qemu everything works fine.
>
> I suspect we can't easily detect whenever qemu is broken or not. Hmm.
>
> Is more than three years being passed enough to just do it
> unconditionally and effectively raise the bar for the minimum
> supported qemu version?
Well, in the other thread ("[PATCH v2] OvmfPkg/PlatformInitLib: catch
QEMU's CPU hotplug reg block regression"), I'm proposing a hard hang for
a QEMU bug that's not been fixed in *any* public release yet, and will
only be fixed in v8 :)
Can you determine the exact QEMU bugfix (commit hash) and the first QEMU
release that included it?
Maybe even build & test that version?
If we determine the minimum functional QEMU version precisely, and it's
like v5 or v6, making it the "official minimum" should be fine.
>
>> (Well, if you mean to keep the same logic for both i440fx adn q35,
>> that's OK then.)
>
> Yes, it would be Uc32Base.
>
> LowMemory and Uc32Base are identical anyway most of the time due to qemu
> preferring gigabyte pages when possible, you need odd memory sizes like
> 1.5 or 2.5 GB to see they actually can be different.
>
Thanks
Laszlo
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