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Subject[RFC 43/55] KVM: arm/arm64: Handle shadow stage 2 page faults
Date
From: Christoffer Dall <christoffer.dall@linaro.org>

If we are faulting on a shadow stage 2 translation, we have to take
extra care in faulting in a page, because we have to collapse the two
levels of stage 2 paging by walking the L2-to-L1 stage 2 page tables in
software.

This approach tries to integrate as much as possible with the existing
code.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
---
arch/arm/include/asm/kvm_emulate.h | 7 ++++
arch/arm/kvm/mmio.c | 12 +++---
arch/arm/kvm/mmu.c | 75 ++++++++++++++++++++++++++++--------
arch/arm64/include/asm/kvm_emulate.h | 9 +++++
4 files changed, 82 insertions(+), 21 deletions(-)

diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
index 6285f4f..dfc53ce 100644
--- a/arch/arm/include/asm/kvm_emulate.h
+++ b/arch/arm/include/asm/kvm_emulate.h
@@ -309,4 +309,11 @@ static inline struct kvm_s2_vmid *vcpu_get_active_vmid(struct kvm_vcpu *vcpu)
{
return &vcpu->kvm->arch.mmu.vmid;
}
+
+/* arm architecture doesn't support the nesting */
+static inline bool kvm_is_shadow_s2_fault(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
#endif /* __ARM_KVM_EMULATE_H__ */
diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
index b6e715f..a1009c2 100644
--- a/arch/arm/kvm/mmio.c
+++ b/arch/arm/kvm/mmio.c
@@ -153,7 +153,7 @@ static int decode_hsr(struct kvm_vcpu *vcpu, bool *is_write, int *len)
}

int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
- phys_addr_t fault_ipa)
+ phys_addr_t ipa)
{
unsigned long data;
unsigned long rt;
@@ -182,22 +182,22 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
data = vcpu_data_guest_to_host(vcpu, vcpu_get_reg(vcpu, rt),
len);

- trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, fault_ipa, data);
+ trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, ipa, data);
kvm_mmio_write_buf(data_buf, len, data);

- ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, fault_ipa, len,
+ ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, ipa, len,
data_buf);
} else {
trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, len,
- fault_ipa, 0);
+ ipa, 0);

- ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, fault_ipa, len,
+ ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, ipa, len,
data_buf);
}

/* Now prepare kvm_run for the potential return to userland. */
run->mmio.is_write = is_write;
- run->mmio.phys_addr = fault_ipa;
+ run->mmio.phys_addr = ipa;
run->mmio.len = len;

if (!ret) {
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 1677a87..710ae60 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -1072,10 +1072,10 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
return ret;
}

-static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, phys_addr_t *ipap)
+static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, gfn_t gfn,
+ phys_addr_t *ipap)
{
kvm_pfn_t pfn = *pfnp;
- gfn_t gfn = *ipap >> PAGE_SHIFT;

if (PageTransCompoundMap(pfn_to_page(pfn))) {
unsigned long mask;
@@ -1291,13 +1291,15 @@ static void coherent_cache_guest_page(struct kvm_vcpu *vcpu, kvm_pfn_t pfn,
}

static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
- struct kvm_memory_slot *memslot, unsigned long hva,
- unsigned long fault_status)
+ struct kvm_s2_trans *nested,
+ 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;
+ phys_addr_t ipa = fault_ipa;
+ gfn_t gfn;
struct kvm *kvm = vcpu->kvm;
struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
struct vm_area_struct *vma;
@@ -1323,9 +1325,23 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
return -EFAULT;
}

- if (is_vm_hugetlb_page(vma) && !logging_active) {
+ if (kvm_is_shadow_s2_fault(vcpu)) {
+ ipa = nested->output;
+
+ /*
+ * If we're about to create a shadow stage 2 entry, then we
+ * can only create huge mapings if the guest hypervior also
+ * uses a huge mapping.
+ */
+ if (nested->block_size != PMD_SIZE)
+ force_pte = true;
+ }
+ gfn = ipa >> PAGE_SHIFT;
+
+
+ if (!force_pte && is_vm_hugetlb_page(vma) && !logging_active) {
hugetlb = true;
- gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
+ gfn = (ipa & PMD_MASK) >> PAGE_SHIFT;
} else {
/*
* Pages belonging to memslots that don't have the same
@@ -1389,7 +1405,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
goto out_unlock;

if (!hugetlb && !force_pte)
- hugetlb = transparent_hugepage_adjust(&pfn, &fault_ipa);
+ hugetlb = transparent_hugepage_adjust(&pfn, gfn, &fault_ipa);

fault_ipa_uncached = memslot->flags & KVM_MEMSLOT_INCOHERENT;

@@ -1435,6 +1451,12 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
kvm_pfn_t pfn;
bool pfn_valid = false;

+ /*
+ * TODO: Lookup nested S2 pgtable entry and if the access flag is set,
+ * then inject an access fault to the guest and invalidate the shadow
+ * entry.
+ */
+
trace_kvm_access_fault(fault_ipa);

spin_lock(&vcpu->kvm->mmu_lock);
@@ -1478,8 +1500,10 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
{
unsigned long fault_status;
- phys_addr_t fault_ipa;
+ phys_addr_t fault_ipa; /* The address we faulted on */
+ phys_addr_t ipa; /* Always the IPA in the L1 guest phys space */
struct kvm_memory_slot *memslot;
+ struct kvm_s2_trans nested_trans;
unsigned long hva;
bool is_iabt, write_fault, writable;
gfn_t gfn;
@@ -1491,7 +1515,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
return 1;
}

- fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
+ ipa = fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);

trace_kvm_guest_fault(*vcpu_pc(vcpu), kvm_vcpu_get_hsr(vcpu),
kvm_vcpu_get_hfar(vcpu), fault_ipa);
@@ -1500,6 +1524,10 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
fault_status = kvm_vcpu_trap_get_fault_type(vcpu);
if (fault_status != FSC_FAULT && fault_status != FSC_PERM &&
fault_status != FSC_ACCESS) {
+ /*
+ * TODO: Report address size faults from an L2 IPA which
+ * exceeds KVM_PHYS_SIZE to the L1 hypervisor.
+ */
kvm_err("Unsupported FSC: EC=%#x xFSC=%#lx ESR_EL2=%#lx\n",
kvm_vcpu_trap_get_class(vcpu),
(unsigned long)kvm_vcpu_trap_get_fault(vcpu),
@@ -1509,7 +1537,23 @@ 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;
+ /*
+ * We may have faulted on a shadow stage 2 page table if we are
+ * running a nested guest. In this case, we have to resovle the L2
+ * IPA to the L1 IPA first, before knowing what kind of memory should
+ * back the L1 IPA.
+ *
+ * If the shadow stage 2 page table walk faults, then we simply inject
+ * this to the guest and carry on.
+ */
+ if (kvm_is_shadow_s2_fault(vcpu)) {
+ ret = kvm_walk_nested_s2(vcpu, fault_ipa, &nested_trans);
+ if (ret)
+ goto out_unlock;
+ ipa = nested_trans.output;
+ }
+
+ gfn = ipa >> PAGE_SHIFT;
memslot = gfn_to_memslot(vcpu->kvm, gfn);
hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
write_fault = kvm_is_write_fault(vcpu);
@@ -1543,13 +1587,13 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
* faulting VA. This is always 12 bits, irrespective
* of the page size.
*/
- fault_ipa |= kvm_vcpu_get_hfar(vcpu) & ((1 << 12) - 1);
- ret = io_mem_abort(vcpu, run, fault_ipa);
+ ipa |= kvm_vcpu_get_hfar(vcpu) & ((1 << 12) - 1);
+ ret = io_mem_abort(vcpu, run, ipa);
goto out_unlock;
}

/* Userspace should not be able to register out-of-bounds IPAs */
- VM_BUG_ON(fault_ipa >= KVM_PHYS_SIZE);
+ VM_BUG_ON(ipa >= KVM_PHYS_SIZE);

if (fault_status == FSC_ACCESS) {
handle_access_fault(vcpu, fault_ipa);
@@ -1557,7 +1601,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
goto out_unlock;
}

- ret = user_mem_abort(vcpu, fault_ipa, memslot, hva, fault_status);
+ ret = user_mem_abort(vcpu, fault_ipa, &nested_trans,
+ memslot, hva, fault_status);
if (ret == 0)
ret = 1;
out_unlock:
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index abad676..2994410 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -368,4 +368,13 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
return data; /* Leave LE untouched */
}

+static inline bool kvm_is_shadow_s2_fault(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_KVM_ARM_NESTED_HYP
+ return (!vcpu_mode_el2(vcpu)) && vcpu_nested_stage2_enabled(vcpu);
+#else
+ return false;
+#endif
+}
+
#endif /* __ARM64_KVM_EMULATE_H__ */
--
1.9.1

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