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

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Date: Tue, 25 Jun 2024 19:12:28 -0500
From: Jeremy Linton <jeremy.linton@....com>
To: Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Steven Price <steven.price@....com>
Cc: kvm@...r.kernel.org, kvmarm@...ts.linux.dev,
 Suzuki K Poulose <suzuki.poulose@....com>,
 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>
Subject: Re: [PATCH v3 02/14] arm64: Detect if in a realm and set RIPAS RAM

Hi,

On 6/12/24 05:40, 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).

To note: i've found out the hard way this set breaks a qemu+kvm+ACPI 
setup as well, for roughly the same reason. I imagine we want kernels 
which can boot in either a realm or a normal guest.

I delayed the version check a bit and then, did enough that 
arm_smcccc_1_1_invoke() could replace arm_smccc_smc() in 
invoke_rsi_fn_smc_with_res(). Which naturally gets it booting again, the 
larger implications i've not considered yet.




> 
> 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
>