linux-kernel - Re: [PATCH v3 13/47] KVM: arm64: Use kernel-space partid configuration for hypercalls

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Message-ID: <1f5206a7-c7e0-4ac1-9921-9baafb596af4@arm.com>
Date: Tue, 13 Jan 2026 14:35:16 +0000
From: Ben Horgan <ben.horgan@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
 baolin.wang@...ux.alibaba.com, carl@...amperecomputing.com,
 dave.martin@....com, david@...nel.org, dfustini@...libre.com,
 fenghuay@...dia.com, gshan@...hat.com, james.morse@....com,
 kobak@...dia.com, lcherian@...vell.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 peternewman@...gle.com, punit.agrawal@....qualcomm.com,
 quic_jiles@...cinc.com, reinette.chatre@...el.com, rohit.mathew@....com,
 scott@...amperecomputing.com, sdonthineni@...dia.com,
 tan.shaopeng@...itsu.com, xhao@...ux.alibaba.com, catalin.marinas@....com,
 will@...nel.org, corbet@....net, maz@...nel.org, oupton@...nel.org,
 joey.gouly@....com, suzuki.poulose@....com, kvmarm@...ts.linux.dev
Subject: Re: [PATCH v3 13/47] KVM: arm64: Use kernel-space partid
 configuration for hypercalls

Hi Jonathan,

On 1/13/26 14:21, Jonathan Cameron wrote:
> On Mon, 12 Jan 2026 16:58:40 +0000
> Ben Horgan <ben.horgan@....com> wrote:
> 
>> On nVHE systems whether or not MPAM is enabled, EL2 continues to use
>> partid-0 for hypercalls, even when the host may have configured its kernel
>> threads to use a different partid. 0 may have been assigned to another
>> task. Copy the EL1 MPAM register to EL2. This ensures hypercalls use the
>> same partid as the kernel thread does on the host.
>>
>> Signed-off-by: Ben Horgan <ben.horgan@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
>> ---
>> Changes since v2:
>> Use mask
>> Use read_sysreg_el1 to cope with hvhe
> 
> nvhe

In this case, I do mean arm64_sw.hvhe which is the configuration when
kvm-arm.mode=protected. The aliasing of the registers when E2H is set
meant that the read_sysreg_s(SYS_MPAM1_EL1) was actually accessing
SYS_MPAM2_EL2 and so the read and write were for the same value.

Thanks,

Ben