Re: [kvm-unit-tests PATCH 1/2] arm64: set sctlr_el1.SPAN

[Nadav Amit <namit@vmware.com>]

> On Jul 18, 2023, at 1:44 AM, Alexandru Elisei <alexandru.elisei@arm.com> wrote:
> 
> Hi,
> 
> On Mon, Jul 17, 2023 at 05:05:06PM +0000, Nadav Amit wrote:
>> Combining the answers to Andrew and Nikos.
>> 
>> On Jul 17, 2023, at 1:53 AM, Nikos Nikoleris <nikos.nikoleris@arm.com> wrote:
>>> 
>>>>> 
>>>>> Would you mind reposting this along with the BSS zeroing patch, the
>>>>> way I proposed we do that, and anything else you've discovered when
>>>>> trying to use the EFI unit tests without QEMU? We'll call that our
>>>>> first non-QEMU EFI support series, since the first EFI series was
>>>>> only targeting QEMU.
>> 
>> I need to rehash the solution that you proposed for BSS (if there is
>> anything special there). I had a different workaround for that issue,
>> because IIRC I had some issues with the zeroing. I’ll give it another
>> 
>>>> 
>>>> Oh, and I meant to mention that, when reposting this patch, maybe we
>>>> can consider managing sctlr in a similar way to the non-efi start path?
>>>> 
>> 
>> I am afraid of turning on random bits on SCTLR. Arguably, the way that
> 
> What do you mean by turning on random bits on SCTLR? All the functional
> bits are documented in the architecture. Same goes for RES1 (it's in the
> Glossary).
> 
>> the non-efi test sets the default value of SCTLR (with no naming of the
>> different bits) is not very friendly.
> 
> That's because as the architecture gets updated, what used to be a RES1 bit
> becomes a functional bit. The only sane way to handle this is to disable
> all the features you don't support, **and** set all the RES1 bits (and
> clear RES0 bits), to disable any newly introduced features you don't know
> about yet which were left enabled by software running at a higher privilege
> level.
> 
> You can send a patch if you want to give a name to the bits which have
> become functional since SCTLR_EL1_RES1 was introduced.

I can give it a quick shot, but I do need to clarify something. Although
I have rather deep knowledge of x86 architecture with over 20 years of
experience, my experience with ARM is limited to 2 weeks. And I don’t even
have an environment in which I can run KVM+ARM.

So I am not inclined to revamp code that was actually just added to
kvm-unit-tests. I will attempt to refactor the code to solve both the
BSS and SCTLR issues in EFI under these limitations.