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    SubjectRe: [RFC PATCH v2 21/26] KVM: arm64: Refactor kvm_arm_setup_stage2()
    On Fri, Jan 08, 2021 at 12:15:19PM +0000, Quentin Perret wrote:
    > In order to re-use some of the stage 2 setup at EL2, factor parts of
    > kvm_arm_setup_stage2() out into static inline functions.
    >
    > No functional change intended.
    >
    > Signed-off-by: Quentin Perret <qperret@google.com>
    > ---
    > arch/arm64/include/asm/kvm_mmu.h | 48 ++++++++++++++++++++++++++++++++
    > arch/arm64/kvm/reset.c | 42 +++-------------------------
    > 2 files changed, 52 insertions(+), 38 deletions(-)
    >
    > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
    > index 662f0415344e..83b4c5cf4768 100644
    > --- a/arch/arm64/include/asm/kvm_mmu.h
    > +++ b/arch/arm64/include/asm/kvm_mmu.h
    > @@ -280,6 +280,54 @@ static inline int kvm_write_guest_lock(struct kvm *kvm, gpa_t gpa,
    > return ret;
    > }
    >
    > +static inline u64 kvm_get_parange(u64 mmfr0)
    > +{
    > + u64 parange = cpuid_feature_extract_unsigned_field(mmfr0,
    > + ID_AA64MMFR0_PARANGE_SHIFT);
    > + if (parange > ID_AA64MMFR0_PARANGE_MAX)
    > + parange = ID_AA64MMFR0_PARANGE_MAX;
    > +
    > + return parange;
    > +}
    > +
    > +/*
    > + * The VTCR value is common across all the physical CPUs on the system.
    > + * We use system wide sanitised values to fill in different fields,
    > + * except for Hardware Management of Access Flags. HA Flag is set
    > + * unconditionally on all CPUs, as it is safe to run with or without
    > + * the feature and the bit is RES0 on CPUs that don't support it.
    > + */
    > +static inline u64 kvm_get_vtcr(u64 mmfr0, u64 mmfr1, u32 phys_shift)
    > +{
    > + u64 vtcr = VTCR_EL2_FLAGS;
    > + u8 lvls;
    > +
    > + vtcr |= kvm_get_parange(mmfr0) << VTCR_EL2_PS_SHIFT;
    > + vtcr |= VTCR_EL2_T0SZ(phys_shift);
    > + /*
    > + * Use a minimum 2 level page table to prevent splitting
    > + * host PMD huge pages at stage2.
    > + */
    > + lvls = stage2_pgtable_levels(phys_shift);
    > + if (lvls < 2)
    > + lvls = 2;
    > + vtcr |= VTCR_EL2_LVLS_TO_SL0(lvls);
    > +
    > + /*
    > + * Enable the Hardware Access Flag management, unconditionally
    > + * on all CPUs. The features is RES0 on CPUs without the support
    > + * and must be ignored by the CPUs.
    > + */
    > + vtcr |= VTCR_EL2_HA;
    > +
    > + /* Set the vmid bits */
    > + vtcr |= (get_vmid_bits(mmfr1) == 16) ?
    > + VTCR_EL2_VS_16BIT :
    > + VTCR_EL2_VS_8BIT;
    > +
    > + return vtcr;
    > +}

    Although I think this is functionally fine, I think it's unusual to see
    large "static inline" functions like this in shared header files. One
    alternative approach would be to follow the example of
    kernel/locking/qspinlock_paravirt.h, where the header is guarded in such a
    way that is only ever included by kernel/locking/qspinlock.c and therefore
    doesn't need the "inline" at all. That separation really helps, I think.

    Will

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