Re: [PATCH RFCv2 3/4] i386/pc: warn if phys-bits is too low

[Joao Martins]

On 2/14/22 15:18, Joao Martins wrote:
> On 2/14/22 15:03, Igor Mammedov wrote:
>> On Mon,  7 Feb 2022 20:24:21 +0000
>> Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>>> Default phys-bits on Qemu is TCG_PHYS_BITS (40) which is enough
>>> to address 1Tb (0xff ffff ffff). On AMD platforms, if a
>>> ram-above-4g relocation happens and the CPU wasn't configured
>>> with a big enough phys-bits, warn the user. There isn't a
>>> catastrophic failure exactly, the guest will still boot, but
>>> most likely won't be able to use more than ~4G of RAM.
>>
>> how 'unable to use" would manifest?
>> It might be better to prevent QEMU startup with broken setup (CLI)
>> rather then letting guest run and trying to figure out what's
>> going wrong when users start to complain. 
>>
> Sounds better to be conservative here.
> 
> I will change from warn_report() to error_report()
> and exit.
> 

I was running through x86_64 qtests prior to submission
and it seems that the inclusion of a pci_hole64_size in
the check added by this patch would break tests if we were
to error out. So far, I'm keeping it as a warning over
compatibility concerns, not limited these 5 test failures
below. Let me know otherwise if you disagree, or if you
prefer another way.

Summary of Failures:

 1/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/qom-test               ERROR       
    0.07s
  killed by signal 6 SIGABRT
 4/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/test-hmp               ERROR       
    0.07s
  killed by signal 6 SIGABRT
 7/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/boot-serial-test       ERROR       
    0.07s
  killed by signal 6 SIGABRT
44/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/test-x86-cpuid-compat  ERROR       
    0.09s
  killed by signal 6 SIGABRT
45/56 qemu:qtest+qtest-x86_64 / qtest-x86_64/numa-test              ERROR       
    0.17s
  killed by signal 6 SIGABRT