[Qemu-devel] [PATCH v3 19/20] kvm: arm64: Allow IPA size supported by the system

[Suzuki K Poulose]

So far we have restricted the IPA size of the VM to the default
value (40bits). Now that we can manage the IPA size per VM and
support dynamic stage2 page tables, allow VMs to have larger IPA.
This is done by setting the IPA limit to the one supported by
the hardware and kernel. This patch also moves the check for
the default IPA size support to kvm_get_ipa_limit().

Since the stage2 page table code is dependent on the stage1
page table, we always ensure that :

  Number of Levels at Stage1 >= Number of Levels at Stage2

So we limit the IPA to make sure that the above condition
is satisfied. This will affect the following combinations
of VA_BITS and IPA for different page sizes.

  39bit VA, 4K  - IPA > 43 (Upto 48)
  36bit VA, 16K - IPA > 40 (Upto 48)
  42bit VA, 64K - IPA > 46 (Upto 52)

Supporting the above combinations need independent stage2
page table manipulation code, which would need substantial
changes. We could purse the solution independently and
switch the page table code once we have it ready.

Cc: Catalin Marinas <address@hidden>
Cc: Marc Zyngier <address@hidden>
Cc: Christoffer Dall <address@hidden>
Signed-off-by: Suzuki K Poulose <address@hidden>
---
Changes since V2:
 - Restrict the IPA size to limit the number of page table
   levels in stage2 to that of stage1 or less.
---
 arch/arm64/include/asm/kvm_host.h |  6 ------
 arch/arm64/include/asm/kvm_mmu.h  | 37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h 
b/arch/arm64/include/asm/kvm_host.h
index 9a15860..e858e49 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -452,13 +452,7 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
 
 static inline void __cpu_init_stage2(void)
 {
-       u32 ps;
-
        kvm_call_hyp(__init_stage2_translation);
-       /* Sanity check for minimum IPA size support */
-       ps = id_aa64mmfr0_parange_to_phys_shift(read_sysreg(id_aa64mmfr0_el1) & 
0x7);
-       WARN_ONCE(ps < 40,
-                 "PARange is %d bits, unsupported configuration!", ps);
 }
 
 /* Guest/host FPSIMD coordination helpers */
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index a291cdc..d38f395 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -547,7 +547,42 @@ static inline void *stage2_alloc_pgd(struct kvm *kvm)
 
 static inline u32 kvm_get_ipa_limit(void)
 {
-       return KVM_PHYS_SHIFT;
+       unsigned int ipa_max, va_max, parange;
+
+       parange = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1) & 0x7;
+       ipa_max = id_aa64mmfr0_parange_to_phys_shift(parange);
+
+       /* Raise the limit to the default size for backward compatibility */
+       if (ipa_max < KVM_PHYS_SHIFT) {
+               WARN_ONCE(1,
+                         "PARange is %d bits, unsupported configuration!",
+                         ipa_max);
+               ipa_max = KVM_PHYS_SHIFT;
+       }
+
+       /* Clamp it to the PA size supported by the kernel */
+       ipa_max = (ipa_max > PHYS_MASK_SHIFT) ? PHYS_MASK_SHIFT : ipa_max;
+       /*
+        * Since our stage2 table is dependent on the stage1 page table code,
+        * we must always honor the following condition:
+        *
+        *  Number of levels in Stage1 >= Number of levels in Stage2.
+        *
+        * So clamp the ipa limit further down to limit the number of levels.
+        * Since we can concatenate upto 16 tables at entry level, we could
+        * go upto 4bits above the maximum VA addressible with the current
+        * number of levels.
+        */
+       va_max = PGDIR_SHIFT + PAGE_SHIFT - 3;
+       va_max += 4;
+
+       if (va_max < ipa_max) {
+               kvm_info("Limiting IPA limit to %dbytes due to host VA bits 
limitation\n",
+                        va_max);
+               ipa_max = va_max;
+       }
+
+       return ipa_max;
 }
 
 static inline void kvm_config_stage2(struct kvm *kvm, u32 ipa_shift)
-- 
2.7.4