Re: [PATCH 14/17] KVM: arm64: Move device mapping management into kvm_s2_fault_pin_pfn()
From: Fuad Tabba <hidden>
Date: 2026-03-17 15:41:57
Also in:
kvmarm
On Mon, 16 Mar 2026 at 17:55, Marc Zyngier [off-list ref] wrote:
Attributes computed for devices are computed very late in the fault handling process, meanning they are mutable for that long. Introduce both 'device' and 'map_non_cacheable' attributes to the vma_info structure, allowing that information to be set in stone earlier, in kvm_s2_fault_pin_pfn(). Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Fuad Tabba <redacted> Cheers, /fuad
quoted hunk ↗ jump to hunk
--- arch/arm64/kvm/mmu.c | 52 ++++++++++++++++++++++++-------------------- 1 file changed, 29 insertions(+), 23 deletions(-)diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index ac4bfcc33aeb1..97cb3585eba03 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c@@ -1656,9 +1656,11 @@ struct kvm_s2_fault_vma_info { struct page *page; kvm_pfn_t pfn; gfn_t gfn; + bool device; bool mte_allowed; bool is_vma_cacheable; bool map_writable; + bool map_non_cacheable; }; static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd,@@ -1728,7 +1730,6 @@ static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd, } struct kvm_s2_fault { - bool s2_force_noncacheable; enum kvm_pgtable_prot prot; };@@ -1738,7 +1739,6 @@ static bool kvm_s2_fault_is_perm(const struct kvm_s2_fault_desc *s2fd) } static int kvm_s2_fault_get_vma_info(const struct kvm_s2_fault_desc *s2fd, - struct kvm_s2_fault *fault, struct kvm_s2_fault_vma_info *s2vi) { struct vm_area_struct *vma;@@ -1794,12 +1794,11 @@ static gfn_t get_canonical_gfn(const struct kvm_s2_fault_desc *s2fd, } static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd, - struct kvm_s2_fault *fault, struct kvm_s2_fault_vma_info *s2vi) { int ret; - ret = kvm_s2_fault_get_vma_info(s2fd, fault, s2vi); + ret = kvm_s2_fault_get_vma_info(s2fd, s2vi); if (ret) return ret;@@ -1814,16 +1813,6 @@ static int kvm_s2_fault_pin_pfn(const struct kvm_s2_fault_desc *s2fd, return -EFAULT; } - return 1; -} - -static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, - struct kvm_s2_fault *fault, - const struct kvm_s2_fault_vma_info *s2vi) -{ - struct kvm *kvm = s2fd->vcpu->kvm; - bool writable = s2vi->map_writable; - /* * Check if this is non-struct page memory PFN, and cannot support * CMOs. It could potentially be unsafe to access as cacheable.@@ -1842,8 +1831,10 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, * S2FWB and CACHE DIC are mandatory to avoid the need for * cache maintenance. */ - if (!kvm_supports_cacheable_pfnmap()) + if (!kvm_supports_cacheable_pfnmap()) { + kvm_release_faultin_page(s2fd->vcpu->kvm, s2vi->page, true, false); return -EFAULT; + } } else { /* * If the page was identified as device early by looking at@@ -1855,9 +1846,24 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, * In both cases, we don't let transparent_hugepage_adjust() * change things at the last minute. */ - fault->s2_force_noncacheable = true; + s2vi->map_non_cacheable = true; } - } else if (memslot_is_logging(s2fd->memslot) && !kvm_is_write_fault(s2fd->vcpu)) { + + s2vi->device = true; + } + + return 1; +} + +static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, + struct kvm_s2_fault *fault, + const struct kvm_s2_fault_vma_info *s2vi) +{ + struct kvm *kvm = s2fd->vcpu->kvm; + bool writable = s2vi->map_writable; + + if (!s2vi->device && memslot_is_logging(s2fd->memslot) && + !kvm_is_write_fault(s2fd->vcpu)) { /* * Only actually map the page as writable if this was a write * fault.@@ -1865,7 +1871,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, writable = false; } - if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && fault->s2_force_noncacheable) + if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu) && s2vi->map_non_cacheable) return -ENOEXEC; /*@@ -1888,7 +1894,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, if (kvm_vcpu_trap_is_exec_fault(s2fd->vcpu)) fault->prot |= KVM_PGTABLE_PROT_X; - if (fault->s2_force_noncacheable) + if (s2vi->map_non_cacheable) fault->prot |= (s2vi->vm_flags & VM_ALLOW_ANY_UNCACHED) ? KVM_PGTABLE_PROT_NORMAL_NC : KVM_PGTABLE_PROT_DEVICE; else if (cpus_have_final_cap(ARM64_HAS_CACHE_DIC))@@ -1897,7 +1903,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, if (s2fd->nested) adjust_nested_exec_perms(kvm, s2fd->nested, &fault->prot); - if (!kvm_s2_fault_is_perm(s2fd) && !fault->s2_force_noncacheable && kvm_has_mte(kvm)) { + if (!kvm_s2_fault_is_perm(s2fd) && !s2vi->map_non_cacheable && kvm_has_mte(kvm)) { /* Check the VMM hasn't introduced a new disallowed VMA */ if (!s2vi->mte_allowed) return -EFAULT;@@ -1937,7 +1943,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd, * backed by a THP and thus use block mapping if possible. */ if (mapping_size == PAGE_SIZE && - !(s2vi->max_map_size == PAGE_SIZE || fault->s2_force_noncacheable)) { + !(s2vi->max_map_size == PAGE_SIZE || s2vi->map_non_cacheable)) { if (perm_fault_granule > PAGE_SIZE) { mapping_size = perm_fault_granule; } else {@@ -1951,7 +1957,7 @@ static int kvm_s2_fault_map(const struct kvm_s2_fault_desc *s2fd, } } - if (!perm_fault_granule && !fault->s2_force_noncacheable && kvm_has_mte(kvm)) + if (!perm_fault_granule && !s2vi->map_non_cacheable && kvm_has_mte(kvm)) sanitise_mte_tags(kvm, pfn, mapping_size); /*@@ -2016,7 +2022,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd) * Let's check if we will get back a huge fault->page backed by hugetlbfs, or * get block mapping for device MMIO region. */ - ret = kvm_s2_fault_pin_pfn(s2fd, &fault, &s2vi); + ret = kvm_s2_fault_pin_pfn(s2fd, &s2vi); if (ret != 1) return ret; --2.47.3