Re: [PATCH v3 02/14] arm64: Detect if in a realm and set RIPAS RAM

[Suzuki K Poulose]

On 12/06/2024 11:40, Jean-Philippe Brucker wrote:
> On Wed, Jun 05, 2024 at 10:29:54AM +0100, Steven Price wrote:
> > From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> >
> > Detect that the VM is a realm guest by the presence of the RSI
> > interface.
> >
> > If in a realm then all memory needs to be marked as RIPAS RAM initially,
> > the loader may or may not have done this for us. To be sure iterate over
> > all RAM and mark it as such. Any failure is fatal as that implies the
> > RAM regions passed to Linux are incorrect - which would mean failing
> > later when attempting to access non-existent RAM.
> >
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > Co-developed-by: Steven Price <steven.price@xxxxxxx>
> > Signed-off-by: Steven Price <steven.price@xxxxxxx>
>
> > +static bool rsi_version_matches(void)
> > +{
> > +	unsigned long ver_lower, ver_higher;
> > +	unsigned long ret = rsi_request_version(RSI_ABI_VERSION,
> > +						&ver_lower,
> > +						&ver_higher);
>
> There is a regression on QEMU TCG (in emulation mode, not running under KVM):
>
>    qemu-system-aarch64 -M virt -cpu max -kernel Image -nographic
>
> This doesn't implement EL3 or EL2, so SMC is UNDEFINED (DDI0487J.a R_HMXQS),
> and we end up with an undef instruction exception. So this patch would
> also break hardware that only implements EL1 (I don't know if it exists).

Thanks for the report,  Could we not check ID_AA64PFR0_EL1.EL3 >= 0 ? I
think we do this for kvm-unit-tests, we need the same here.


Suzuki

> The easiest fix is to detect the SMC conduit through the PSCI node in DT.
> SMCCC helpers already do this, but we can't use them this early in the
> boot. I tested adding an early probe to the PSCI driver to check this, see
> attached patches.
>
> Note that we do need to test the conduit after finding a PSCI node,
> because even though it doesn't implement EL2 in this configuration, QEMU
> still accepts PSCI HVCs in order to support SMP.
>
> Thanks,
> Jean