Re: [kvm-unit-tests PATCH v2] arm64: Add basic MTE test

[Andrew Jones <andrew.jones@linux.dev>]

On Thu, Jan 02, 2025 at 12:27:43PM +0000, Alexandru Elisei wrote:
> Hi Drew,
> 
> On Mon, Dec 30, 2024 at 05:52:54PM +0100, Andrew Jones wrote:
> > On Mon, Dec 30, 2024 at 04:28:30PM +0000, Alexandru Elisei wrote:
> > > Hi Drew,
> > > 
> > > On Mon, Dec 30, 2024 at 04:45:01PM +0100, Andrew Jones wrote:
> > > > On Mon, Dec 30, 2024 at 03:19:48PM +0000, Alexandru Elisei wrote:
> > > > ...
> > > > > Interestingly though, when I try to run a test (either with ./run_tests.sh
> > > > > mte-sync, or by trying out your example), I get this error:
> > > > > 
> > > > > qemu-system-aarch64: MTE requested, but not supported by the guest CPU
> > > > > 
> > > > > My guess is that's caused by kvm-unit-tests defaulting to cortex-a57 as the
> > > > > model CPU. Changing the cpu to 'max' makes the test run. How are you getting
> > > > > around this on your end?
> > > > >
> > > > 
> > > > We can (and I think should) change to 'max' for the default model.
> > > 
> > > I think so too, something like this maybe?
> > > 
> > > diff --git a/configure b/configure
> > > index 86cf1da36467..4babbd5f5e74 100755
> > > --- a/configure
> > > +++ b/configure
> > > @@ -286,7 +286,7 @@ fi
> > >  [ -z "$processor" ] && processor="$arch"
> > > 
> > >  if [ "$processor" = "arm64" ]; then
> > > -    processor="cortex-a57"
> > > +    processor="max"
> > >  elif [ "$processor" = "arm" ]; then
> > >      processor="cortex-a15"
> > >  fi
> > > 
> > > Can't do the same for arm, because Makefile.arm passes the processor to
> > > -mcpu and that causes a build error.
> > 
> > I wonder if we can improve the mcpu thing by just selecting some generic
> > cpu type at this point? Or just dropping it and counting on the compiler
> > to use generic cpu type? It'd be nice to use max for both arm and arm64,
> 
> I tried setting the default to 'max' for both arm and arm64. If I pass
> 'max' as the cpu type to arm, I get the build error above. If I don't pass
> -mcpu to the arm compiler when $PROCESSOR=max, I get different errors
> because of unsupported instructions:
> 
> /tmp/ccOHIrg7.s: Assembler messages:
> /tmp/ccOHIrg7.s:46: Error: selected processor does not support `yield' in ARM mode
> /tmp/ccGCB0zP.s: Assembler messages:
> /tmp/ccGCB0zP.s:55: Error: selected processor does not support `ldrex r2,[r4]' in ARM mode
> /tmp/ccGCB0zP.s:59: Error: selected processor does not support `strex r3,r2,[r4]' in ARM mode
> /tmp/ccGCB0zP.s:71: Error: selected processor does not support `dmb ish' in ARM mode
> /tmp/ccGCB0zP.s:99: Error: selected processor does not support `dmb ish' in ARM mode
> /tmp/ccGCB0zP.s:144: Error: selected processor does not support `dmb ish' in ARM mode
> [..]
> 
> and the errors go on. This means that the default cannot be 'max' for arm.
> 
> I also realized that the configure --processor option for arm64:
> 
>    --processor=PROCESSOR  processor to compile for (aarch64)
> 
> does not work as advertised, because the $PROCESSOR variable is not passed
> down to the compiler.
> 
> So what I'm proposing is this:
> 
> - Patch #1: pass $PROCESSOR to the arm64 compiler, to reconcile the help
>   text for --processor and to achieve parity with arm.
> 
> - Patch #2: have arm64 ignore $PROCESSOR when compiling if it's 'max.  By
>   ignore I mean don't add a -mcpu argument to the compiler invocation.
>   Change configure to raise an error if --processor=max is used for arm
>   (users might think that if it works for arm64, it also works for arm).
> 
> - Patch #3: change the default for arm64 to 'max', but don't touch the
>   default for arm.
> 
> What do you think?

Works for me.

Thanks,
drew

> 
> Thanks,
> Alex
> 
> > but if nobody has time to do the arm work / testing to be sure we can,
> > then I'm fine with just a patch changing arm64.
> > 
> > Thanks,
> > drew