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

From: Igor Mammedov <imammedo@redhat.com>
To: Joao Martins <joao.m.martins@oracle.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	qemu-devel@nongnu.org, Daniel Jordan <daniel.m.jordan@oracle.com>,
	David Edmondson <david.edmondson@oracle.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Ani Sinha <ani@anisinha.ca>, Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH RFCv2 3/4] i386/pc: warn if phys-bits is too low
Date: Thu, 24 Feb 2022 10:01:38 +0100	[thread overview]
Message-ID: <20220224100138.0ddab7b9@redhat.com> (raw)
In-Reply-To: <04efb316-e231-7abd-0eb6-5b0241afd5f2@oracle.com>

On Wed, 23 Feb 2022 17:18:55 +0000
Joao Martins <joao.m.martins@oracle.com> wrote:

> 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.

can you check what exactly breaks tests?

> 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
> 