* [PATCH v15 15/21] KVM: arm64: Refactor user_mem_abort()
2025-07-17 16:27 [PATCH v15 00/21] KVM: Enable host userspace mapping for guest_memfd-backed memory for non-CoCo VMs Fuad Tabba
@ 2025-07-17 16:27 ` Fuad Tabba
0 siblings, 0 replies; 2+ messages in thread
From: Fuad Tabba @ 2025-07-17 16:27 UTC (permalink / raw)
To: kvm, linux-arm-msm, linux-mm, kvmarm
Cc: pbonzini, chenhuacai, mpe, anup, paul.walmsley, palmer, aou,
seanjc, viro, brauner, willy, akpm, xiaoyao.li, yilun.xu,
chao.p.peng, jarkko, amoorthy, dmatlack, isaku.yamahata, mic,
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quic_tsoni, quic_svaddagi, quic_cvanscha, quic_pderrin,
quic_pheragu, catalin.marinas, james.morse, yuzenghui,
oliver.upton, maz, will, qperret, keirf, roypat, shuah, hch, jgg,
rientjes, jhubbard, fvdl, hughd, jthoughton, peterx, pankaj.gupta,
ira.weiny, tabba
Refactor user_mem_abort() to improve code clarity and simplify
assumptions within the function.
Key changes include:
* Immediately set force_pte to true at the beginning of the function if
logging_active is true. This simplifies the flow and makes the
condition for forcing a PTE more explicit.
* Remove the misleading comment stating that logging_active is
guaranteed to never be true for VM_PFNMAP memslots, as this assertion
is not entirely correct.
* Extract reusable code blocks into new helper functions:
* prepare_mmu_memcache(): Encapsulates the logic for preparing and
topping up the MMU page cache.
* adjust_nested_fault_perms(): Isolates the adjustments to shadow S2
permissions and the encoding of nested translation levels.
* Update min(a, (long)b) to min_t(long, a, b) for better type safety and
consistency.
* Perform other minor tidying up of the code.
These changes primarily aim to simplify user_mem_abort() and make its
logic easier to understand and maintain, setting the stage for future
modifications.
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
arch/arm64/kvm/mmu.c | 110 +++++++++++++++++++++++--------------------
1 file changed, 59 insertions(+), 51 deletions(-)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 2942ec92c5a4..b3eacb400fab 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1470,13 +1470,56 @@ static bool kvm_vma_mte_allowed(struct vm_area_struct *vma)
return vma->vm_flags & VM_MTE_ALLOWED;
}
+static int prepare_mmu_memcache(struct kvm_vcpu *vcpu, bool topup_memcache,
+ void **memcache)
+{
+ int min_pages;
+
+ if (!is_protected_kvm_enabled())
+ *memcache = &vcpu->arch.mmu_page_cache;
+ else
+ *memcache = &vcpu->arch.pkvm_memcache;
+
+ if (!topup_memcache)
+ return 0;
+
+ min_pages = kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu);
+
+ if (!is_protected_kvm_enabled())
+ return kvm_mmu_topup_memory_cache(*memcache, min_pages);
+
+ return topup_hyp_memcache(*memcache, min_pages);
+}
+
+/*
+ * Potentially reduce shadow S2 permissions to match the guest's own S2. For
+ * exec faults, we'd only reach this point if the guest actually allowed it (see
+ * kvm_s2_handle_perm_fault).
+ *
+ * Also encode the level of the original translation in the SW bits of the leaf
+ * entry as a proxy for the span of that translation. This will be retrieved on
+ * TLB invalidation from the guest and used to limit the invalidation scope if a
+ * TTL hint or a range isn't provided.
+ */
+static void adjust_nested_fault_perms(struct kvm_s2_trans *nested,
+ enum kvm_pgtable_prot *prot,
+ bool *writable)
+{
+ *writable &= kvm_s2_trans_writable(nested);
+ if (!kvm_s2_trans_readable(nested))
+ *prot &= ~KVM_PGTABLE_PROT_R;
+
+ *prot |= kvm_encode_nested_level(nested);
+}
+
static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
struct kvm_s2_trans *nested,
struct kvm_memory_slot *memslot, unsigned long hva,
bool fault_is_perm)
{
int ret = 0;
- bool write_fault, writable, force_pte = false;
+ bool topup_memcache;
+ bool write_fault, writable;
bool exec_fault, mte_allowed;
bool device = false, vfio_allow_any_uc = false;
unsigned long mmu_seq;
@@ -1488,6 +1531,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
gfn_t gfn;
kvm_pfn_t pfn;
bool logging_active = memslot_is_logging(memslot);
+ bool force_pte = logging_active;
long vma_pagesize, fault_granule;
enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
struct kvm_pgtable *pgt;
@@ -1498,17 +1542,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
fault_granule = kvm_vcpu_trap_get_perm_fault_granule(vcpu);
write_fault = kvm_is_write_fault(vcpu);
exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu);
- VM_BUG_ON(write_fault && exec_fault);
-
- if (fault_is_perm && !write_fault && !exec_fault) {
- kvm_err("Unexpected L2 read permission error\n");
- return -EFAULT;
- }
-
- if (!is_protected_kvm_enabled())
- memcache = &vcpu->arch.mmu_page_cache;
- else
- memcache = &vcpu->arch.pkvm_memcache;
+ VM_WARN_ON_ONCE(write_fault && exec_fault);
/*
* Permission faults just need to update the existing leaf entry,
@@ -1516,17 +1550,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
* only exception to this is when dirty logging is enabled at runtime
* and a write fault needs to collapse a block entry into a table.
*/
- if (!fault_is_perm || (logging_active && write_fault)) {
- int min_pages = kvm_mmu_cache_min_pages(vcpu->arch.hw_mmu);
-
- if (!is_protected_kvm_enabled())
- ret = kvm_mmu_topup_memory_cache(memcache, min_pages);
- else
- ret = topup_hyp_memcache(memcache, min_pages);
-
- if (ret)
- return ret;
- }
+ topup_memcache = !fault_is_perm || (logging_active && write_fault);
+ ret = prepare_mmu_memcache(vcpu, topup_memcache, &memcache);
+ if (ret)
+ return ret;
/*
* Let's check if we will get back a huge page backed by hugetlbfs, or
@@ -1540,16 +1567,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
return -EFAULT;
}
- /*
- * logging_active is guaranteed to never be true for VM_PFNMAP
- * memslots.
- */
- if (logging_active) {
- force_pte = true;
+ if (force_pte)
vma_shift = PAGE_SHIFT;
- } else {
+ else
vma_shift = get_vma_page_shift(vma, hva);
- }
switch (vma_shift) {
#ifndef __PAGETABLE_PMD_FOLDED
@@ -1601,7 +1622,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
max_map_size = PAGE_SIZE;
force_pte = (max_map_size == PAGE_SIZE);
- vma_pagesize = min(vma_pagesize, (long)max_map_size);
+ vma_pagesize = min_t(long, vma_pagesize, max_map_size);
}
/*
@@ -1630,7 +1651,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
* Rely on mmap_read_unlock() for an implicit smp_rmb(), which pairs
* with the smp_wmb() in kvm_mmu_invalidate_end().
*/
- mmu_seq = vcpu->kvm->mmu_invalidate_seq;
+ mmu_seq = kvm->mmu_invalidate_seq;
mmap_read_unlock(current->mm);
pfn = __kvm_faultin_pfn(memslot, gfn, write_fault ? FOLL_WRITE : 0,
@@ -1665,24 +1686,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (exec_fault && device)
return -ENOEXEC;
- /*
- * Potentially reduce shadow S2 permissions to match the guest's own
- * S2. For exec faults, we'd only reach this point if the guest
- * actually allowed it (see kvm_s2_handle_perm_fault).
- *
- * Also encode the level of the original translation in the SW bits
- * of the leaf entry as a proxy for the span of that translation.
- * This will be retrieved on TLB invalidation from the guest and
- * used to limit the invalidation scope if a TTL hint or a range
- * isn't provided.
- */
- if (nested) {
- writable &= kvm_s2_trans_writable(nested);
- if (!kvm_s2_trans_readable(nested))
- prot &= ~KVM_PGTABLE_PROT_R;
-
- prot |= kvm_encode_nested_level(nested);
- }
+ if (nested)
+ adjust_nested_fault_perms(nested, &prot, &writable);
kvm_fault_lock(kvm);
pgt = vcpu->arch.hw_mmu->pgt;
@@ -1953,6 +1958,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
goto out_unlock;
}
+ VM_WARN_ON_ONCE(kvm_vcpu_trap_is_permission_fault(vcpu) &&
+ !write_fault && !kvm_vcpu_trap_is_exec_fault(vcpu));
+
ret = user_mem_abort(vcpu, fault_ipa, nested, memslot, hva,
esr_fsc_is_permission_fault(esr));
if (ret == 0)
--
2.50.0.727.gbf7dc18ff4-goog
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