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Message-ID: <20240613105107.GC417776@myrica>
Date: Thu, 13 Jun 2024 11:51:07 +0100
From: Jean-Philippe Brucker <jean-philippe@...aro.org>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Steven Price <steven.price@....com>, kvm@...r.kernel.org,
kvmarm@...ts.linux.dev, Catalin Marinas <catalin.marinas@....com>,
Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
James Morse <james.morse@....com>,
Oliver Upton <oliver.upton@...ux.dev>,
Zenghui Yu <yuzenghui@...wei.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Joey Gouly <joey.gouly@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
Christoffer Dall <christoffer.dall@....com>,
Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
peter.maydell@...aro.org
Subject: Re: [PATCH v3 02/14] arm64: Detect if in a realm and set RIPAS RAM
On Wed, Jun 12, 2024 at 11:59:22AM +0100, Suzuki K Poulose wrote:
> 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@....com>
> > >
> > > 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@....com>
> > > Co-developed-by: Steven Price <steven.price@....com>
> > > Signed-off-by: Steven Price <steven.price@....com>
> >
> > > +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.
Good point, it also fixes this case and is simpler. It assumes RMM doesn't
hide this field, but I can't think of a reason it would.
This command won't work anymore:
qemu-system-aarch64 -M virt,secure=on -cpu max -kernel Image -nographic
implements EL3 and SMC still treated as undef. QEMU has a special case for
starting at EL2 in this case, but I couldn't find what this is for.
Treating SMC as undef is correct because SCR_EL3.SMD resets to an
architectutally UNKNOWN value. But the architecture requires that the CPU
resets to the highest implemented exception level (DDI0487J.a R_JYLQV). So
in my opinion we can use the ID_AA64PFR0_EL1.EL3 field here, and breaking
this particular configuration is not a problem: users shouldn't expect
Linux to boot when EL3 is implemented and doesn't run a firmware.
Thanks,
Jean
>
>
> 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
> >
>
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