arm/arm64: KVM: Support KVM_CAP_READONLY_MEM

When userspace loads code and data in a read-only memory regions, KVM
needs to be able to handle this on arm and arm64.  Specifically this is
used when running code directly from a read-only flash device; the
common scenario is a UEFI blob loaded with the -bios option in QEMU.

Note that the MMIO exit on writes to a read-only memory is ABI and can
be used to emulate block-erase style flash devices.

Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

4 files changed, 11 insertions, 14 deletions

diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
index e6ebdd3471e5..51257fda254b 100644
--- a/arch/arm/include/uapi/asm/kvm.h
+++ b/arch/arm/include/uapi/asm/kvm.h
@@ -25,6 +25,7 @@
 
 #define __KVM_HAVE_GUEST_DEBUG
 #define __KVM_HAVE_IRQ_LINE
+#define __KVM_HAVE_READONLY_MEM
 
 #define KVM_REG_SIZE(id)                                                \
         (1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index 9f788ebac55b..ac306b4dbe1d 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -188,6 +188,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
         case KVM_CAP_ONE_REG:
         case KVM_CAP_ARM_PSCI:
         case KVM_CAP_ARM_PSCI_0_2:
+        case KVM_CAP_READONLY_MEM:
                 r = 1;
                 break;
         case KVM_CAP_COALESCED_MMIO:
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 16e7994bf347..62f5642153f9 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -747,14 +747,13 @@ static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
 }
 
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
-                          struct kvm_memory_slot *memslot,
+                          struct kvm_memory_slot *memslot, unsigned long hva,
                           unsigned long fault_status)
 {
         int ret;
         bool write_fault, writable, hugetlb = false, force_pte = false;
         unsigned long mmu_seq;
         gfn_t gfn = fault_ipa >> PAGE_SHIFT;
-        unsigned long hva = gfn_to_hva(vcpu->kvm, gfn);
         struct kvm *kvm = vcpu->kvm;
         struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
         struct vm_area_struct *vma;
@@ -863,7 +862,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
         unsigned long fault_status;
         phys_addr_t fault_ipa;
         struct kvm_memory_slot *memslot;
-        bool is_iabt;
+        unsigned long hva;
+        bool is_iabt, write_fault, writable;
         gfn_t gfn;
         int ret, idx;
 
@@ -884,7 +884,10 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
         idx = srcu_read_lock(&vcpu->kvm->srcu);
 
         gfn = fault_ipa >> PAGE_SHIFT;
-        if (!kvm_is_visible_gfn(vcpu->kvm, gfn)) {
+        memslot = gfn_to_memslot(vcpu->kvm, gfn);
+        hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
+        write_fault = kvm_is_write_fault(kvm_vcpu_get_hsr(vcpu));
+        if (kvm_is_error_hva(hva) || (write_fault && !writable)) {
                 if (is_iabt) {
                         /* Prefetch Abort on I/O address */
                         kvm_inject_pabt(vcpu, kvm_vcpu_get_hfar(vcpu));
@@ -892,13 +895,6 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
                         goto out_unlock;
                 }
 
-                if (fault_status != FSC_FAULT) {
-                        kvm_err("Unsupported fault status on io memory: %#lx\n",
-                                fault_status);
-                        ret = -EFAULT;
-                        goto out_unlock;
-                }
-
                 /*
                  * The IPA is reported as [MAX:12], so we need to
                  * complement it with the bottom 12 bits from the
@@ -910,9 +906,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
                 goto out_unlock;
         }
 
-        memslot = gfn_to_memslot(vcpu->kvm, gfn);
-
-        ret = user_mem_abort(vcpu, fault_ipa, memslot, fault_status);
+        ret = user_mem_abort(vcpu, fault_ipa, memslot, hva, fault_status);
         if (ret == 0)
                 ret = 1;
 out_unlock:
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index e633ff8cdec8..f4ec5a674d05 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -37,6 +37,7 @@
 
 #define __KVM_HAVE_GUEST_DEBUG
 #define __KVM_HAVE_IRQ_LINE
+#define __KVM_HAVE_READONLY_MEM
 
 #define KVM_REG_SIZE(id)                                                \
         (1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))