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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 16:47:28 +0000

On Fri, 27 Nov 2020 at 16:38, Peter Maydell <peter.maydell@linaro.org> wrote:
> Having looked a bit more closely at some of the relevant target/arm
> code, I think the best approach is going to be that in virt.c
> we just check the PARange ID register field (probably via
> a convenience function that does the conversion of that to
> a nice number-of-bits return value; we might even have one
> already).

Ha, in fact we're already doing something quite close to this,
though instead of saying "decide whether to use highmem based
on the CPU's PA range" we go for "report error to user if PA
range is insufficient" and let the user pick some command line
options that disable highmem if they want:

        if (aarch64 && vms->highmem) {
            int requested_pa_size = 64 - clz64(vms->highest_gpa);
            int pamax = arm_pamax(ARM_CPU(first_cpu));

            if (pamax < requested_pa_size) {
                error_report("VCPU supports less PA bits (%d) than "
                             "requested by the memory map (%d)",
                             pamax, requested_pa_size);

-- PMM

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