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Re: [PATCH 8/8] hw/arm/virt: Disable highmem when on hypervisor.framewor

From: Peter Maydell
Subject: Re: [PATCH 8/8] hw/arm/virt: Disable highmem when on hypervisor.framework
Date: Fri, 27 Nov 2020 18:16:27 +0000

On Fri, 27 Nov 2020 at 17:18, Eduardo Habkost <ehabkost@redhat.com> wrote:
> Thanks!  Is the data returned by kvm_arm_get_host_cpu_features()
> supposed to eventually affect the value of id_aa64mmfr0?  I don't
> see how that could happen.

kvm_arm_get_host_cpu_features() does:
        err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64mmfr0,
                              ARM64_SYS_REG(3, 0, 0, 7, 0));

which is filling in data in the ARMHostCPUFeatures* that it is
passed as an argument. The caller is kvm_arm_set_cpu_features_from_host(),
which does
(assuming it hasn't already done it once and cached the results;
arm_host_cpu_features is a global) and then
 cpu->isar = arm_host_cpu_features.isar;
thus copying the ID values into the "struct ARMISARegisters isar"
that is part of the ARMCPU struct. (It also copies across the
'features' word which gets set up with ARM_FEATURE_* flags
for the benefit of the parts of the target code which key off
those rather than ID register fields.)

-- PMM

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