Re: [kvm-unit-tests PATCH v3 15/27] arm/arm64: mmu_disable: Clean and invalidate before disabling

Alexandru Elisei
2022-07-11T14:23:02Z

Hi Drew,

Sorry, I lost track of this thread.

On Fri, Jul 01, 2022 at 01:16:27PM +0200, Andrew Jones wrote:
> On Fri, Jul 01, 2022 at 11:24:44AM +0100, Alexandru Elisei wrote:
> ...
> > > being dropped and replaced by one of you with something that "makes
> > > more sense" as long as the outcome (coherent execution on bare-metal)
> > > still works.
> >
> > Hmm... maybe an experiment will work. I propose the following:
> >
> > 1. Revert this patch.
> > 2. Apply this diff on top of the series:
> >
> > diff --git a/lib/arm/setup.c b/lib/arm/setup.c
> > index 30d04d0eb100..913f4088d96c 100644
> > --- a/lib/arm/setup.c
> > +++ b/lib/arm/setup.c
> > @@ -374,6 +374,11 @@ static efi_status_t efi_mem_init(efi_bootinfo_t *efi_bootinfo)
> > }
> > }
> > __phys_end &= PHYS_MASK;
> > +
> > + asm volatile("dc cvau, %0\n" :: "r" (&__phys_offset) : "memory");
> > + asm volatile("dc cvau, %0\n" :: "r" (&__phys_end) : "memory");
> > + dsb(sy);
> > +
> > asm_mmu_disable();
> >
> > if (free_mem_pages == 0)
> >
> > This is the solution, based on an architectural explanation of what we were
> > observing, that I proposed on your github branch, a solution that you've
> > tested with the result:
> >
> > "I tested at least 10 times (lost count) with a build where "arm/arm64:
> > mmu_disable: Clean and invalidate before disabling" was reverted from the
> > target-efi branch and your hack was applied. It worked every time."
> >
> > [1] https://github.com/rhdrjones/kvm-unit-tests/commit/fc58684bc47b7d07d75098fdfddb6083e9b12104#commitcomment-44222926
> >
>
> Hi Alex,
>
> Thanks for digging that back up. I had lost track of it. The last comment
> is you saying that you'll send a proper patch. Did you send one that got
> lost? If not, would you like to send one now that Nikos can incorporate?

The "proper patch" that I was referring to was to skip cache maintenance
when the MMU is already off. Based on the ongoing thread with Nikos, we
might have to rethink asm_mmu_disable, so I'm waiting for a conclusion
before I make any changes to asm_mmu_disable.

Thanks,
Alex

>
> Thanks,
> drew