Re: [PATCH v2 9/9] accel/mshv: disable la57 (5lvl paging)

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Wed, Mar 11, 2026 at 04:31:41PM +0100, Mohamed Mediouni wrote:
> Thank you, I’ll test this further. Boot-tested it on an Alpine Linux VM but looks like
> that wasn’t enough...
> 
> FYI I added a new callback interface in x86_emul_ops (mmu_gva_to_gpa) to support
> adding the Hyper-V page table walker, but if it’s anything like the WHP one it’s going to
> be very slow… which is why I moved to the new interface in the first place.

hmm, I quickly tried that and implemented a hook like this:

static MMUTranslateResult gva_to_gpa(CPUState *cpu, target_ulong gva,
                                     uint64_t *gpa, MMUTranslateFlags flags)
{
    uint64_t hv_flags = 0;

    if (!x86_is_paging_mode(cpu)) {
        *gpa = gva;

        return MMU_TRANSLATE_SUCCESS;
    }

    if (flags & MMU_TRANSLATE_VALIDATE_WRITE) {
        hv_flags = HV_TRANSLATE_GVA_VALIDATE_WRITE;
    } else if (flags & MMU_TRANSLATE_VALIDATE_EXECUTE) {
        hv_flags = HV_TRANSLATE_GVA_VALIDATE_EXECUTE;
    } else {
        hv_flags = HV_TRANSLATE_GVA_VALIDATE_READ;
    }

    if (translate_gva(cpu, gva, gpa, hv_flags) < 0) {
        return MMU_TRANSLATE_PAGE_NOT_MAPPED;
    }

    return MMU_TRANSLATE_SUCCESS;
}

static const struct x86_emul_ops mshv_x86_emul_ops = {
    .read_segment_descriptor = read_segment_descriptor,
    .mmu_gva_to_gpa = gva_to_gpa,
};

but without explicitly disabling la57, I still see the same MMIO errors
during guest boot (ubuntu jammy). probably needs more investigation. I
think for now disabling la57 seems ok.