On Wednesday 03 Feb 2021 at 15:53:54 (+0000), Will Deacon wrote:

On Fri, Jan 08, 2021 at 12:15:19PM +0000, Quentin Perret wrote:

quoted

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 <redacted>
---
 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.

Alternatively, I might be able to have an mmu.c file in the hyp/ folder,
and to compile it for both the host kernel and the EL2 obj as we do for
a few things already. Or maybe I'll just stick it in pgtable.c. Either
way, it'll add a function call, but I can't really see that having any
measurable impact, so we should be fine.

Cheers,
Quentin

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