KVM: arm64: Rename the device variable to s2_force_noncacheable

To perform cache maintenance on a region of memory, KVM/arm64 relies on
that region having a cacheable alias in the kernel's address space which
can be used with CMO instructions.

The 'device' variable is somewhat of a misnomer, as it actually
indicates whether or not the stage-2 alias is allowed to have cacheable
memory attributes. The resulting stage-2 memory attributes are further
modified by VM_ALLOW_ANY_UNCACHED, selecting between Normal-NC or
Device-nGnRE depending on what the endpoint supports.

Rename the to s2_force_noncacheable such that its purpose is a bit more
obvious.

CC: Catalin Marinas <catalin.marinas@arm.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Tested-by: Donald Dutile <ddutile@redhat.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20250705071717.5062-2-ankita@nvidia.com
[ Oliver: addressed typos, wound up rewriting changelog ]
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 2942ec92c5a4a2746a94837c1e98a178ff98ff6f..1601ab9527d44646c79a299cfa425ab03056f925 100644 (file)
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1478,7 +1478,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
        int ret = 0;
        bool write_fault, writable, force_pte = false;
        bool exec_fault, mte_allowed;
-       bool device = false, vfio_allow_any_uc = false;
+       bool s2_force_noncacheable = false, vfio_allow_any_uc = false;
        unsigned long mmu_seq;
        phys_addr_t ipa = fault_ipa;
        struct kvm *kvm = vcpu->kvm;
@@ -1653,7 +1653,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                 * In both cases, we don't let transparent_hugepage_adjust()
                 * change things at the last minute.
                 */
-               device = true;
+               s2_force_noncacheable = true;
        } else if (logging_active && !write_fault) {
                /*
                 * Only actually map the page as writable if this was a write
@@ -1662,7 +1662,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                writable = false;
        }
 
-       if (exec_fault && device)
+       if (exec_fault && s2_force_noncacheable)
                return -ENOEXEC;
 
        /*
@@ -1695,7 +1695,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
         * If we are not forced to use page mapping, check if we are
         * backed by a THP and thus use block mapping if possible.
         */
-       if (vma_pagesize == PAGE_SIZE && !(force_pte || device)) {
+       if (vma_pagesize == PAGE_SIZE && !(force_pte || s2_force_noncacheable)) {
                if (fault_is_perm && fault_granule > PAGE_SIZE)
                        vma_pagesize = fault_granule;
                else
@@ -1709,7 +1709,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                }
        }
 
-       if (!fault_is_perm && !device && kvm_has_mte(kvm)) {
+       if (!fault_is_perm && !s2_force_noncacheable && kvm_has_mte(kvm)) {
                /* Check the VMM hasn't introduced a new disallowed VMA */
                if (mte_allowed) {
                        sanitise_mte_tags(kvm, pfn, vma_pagesize);
@@ -1725,7 +1725,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
        if (exec_fault)
                prot |= KVM_PGTABLE_PROT_X;
 
-       if (device) {
+       if (s2_force_noncacheable) {
                if (vfio_allow_any_uc)
                        prot |= KVM_PGTABLE_PROT_NORMAL_NC;
                else