[PATCH v9 2/6] KVM: arm64: Update the check to detect device memory

ankita
2025-06-21T04:32:54Z

From: Ankit Agrawal <ankita@nvidia.com>

Currently, the kvm_is_device_pfn() detects if the memory is kernel
mapped through pfn_is_map_memory. It thus implies whether KVM can
use Cache Maintenance Operations (CMOs) on that PFN. It is a bit
of a misnomer as it does not necessarily detect whether a PFN
is for a device memory. Moreover, the function is only used at
one place.

It would be better to directly call pfn_is_map_memory. Moreover
we should restrict this call to VM_PFNMAP or VM_MIXEDMAP. Otherwise
the VMA has struct pages in it and mapped in the kernel VA.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Ankit Agrawal <ankita@nvidia.com>
---
arch/arm64/kvm/mmu.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 1601ab9527d4..5fe24f30999d 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -193,11 +193,6 @@ int kvm_arch_flush_remote_tlbs_range(struct kvm *kvm,
return 0;
}

-static bool kvm_is_device_pfn(unsigned long pfn)
-{
- return !pfn_is_map_memory(pfn);
-}
-
static void *stage2_memcache_zalloc_page(void *arg)
{
struct kvm_mmu_memory_cache *mc = arg;
@@ -1492,6 +1487,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
struct kvm_pgtable *pgt;
struct page *page;
+ vm_flags_t vm_flags;
enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_HANDLE_FAULT | KVM_PGTABLE_WALK_SHARED;

if (fault_is_perm)
@@ -1619,6 +1615,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,

vfio_allow_any_uc = vma->vm_flags & VM_ALLOW_ANY_UNCACHED;

+ vm_flags = vma->vm_flags;
+
/* Don't use the VMA after the unlock -- it may have vanished */
vma = NULL;

@@ -1642,7 +1640,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
if (is_error_noslot_pfn(pfn))
return -EFAULT;

- if (kvm_is_device_pfn(pfn)) {
+ if (vm_flags & (VM_PFNMAP | VM_MIXEDMAP) && !pfn_is_map_memory(pfn)) {
/*
* If the page was identified as device early by looking at
* the VMA flags, vma_pagesize is already representing the
--
2.34.1