[PATCH v2 2/7] KVM: arm64: Simplify the sanitise_mte_tags() logic

Peter Collingbourne
2022-07-22T01:51:03Z

From: Catalin Marinas <catalin.marinas@arm.com>

Currently sanitise_mte_tags() checks if it's an online page before
attempting to sanitise the tags. Such detection should be done in the
caller via the VM_MTE_ALLOWED vma flag. Since kvm_set_spte_gfn() does
not have the vma, leave the page unmapped if not already tagged. Tag
initialisation will be done on a subsequent access fault in
user_mem_abort().

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
---
arch/arm64/kvm/mmu.c | 40 +++++++++++++++-------------------------
1 file changed, 15 insertions(+), 25 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index c9012707f69c..1a3707aeb41f 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1056,23 +1056,14 @@ static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva)
* - mmap_lock protects between a VM faulting a page in and the VMM performing
* an mprotect() to add VM_MTE
*/
-static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
- unsigned long size)
+static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
+ unsigned long size)
{
unsigned long i, nr_pages = size >> PAGE_SHIFT;
- struct page *page;
+ struct page *page = pfn_to_page(pfn);

if (!kvm_has_mte(kvm))
- return 0;
-
- /*
- * pfn_to_online_page() is used to reject ZONE_DEVICE pages
- * that may not support tags.
- */
- page = pfn_to_online_page(pfn);
-
- if (!page)
- return -EFAULT;
+ return;

for (i = 0; i < nr_pages; i++, page++) {
if (!page_mte_tagged(page)) {
@@ -1080,8 +1071,6 @@ static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
set_page_mte_tagged(page);
}
}
-
- return 0;
}

static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
@@ -1092,7 +1081,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
bool write_fault, writable, force_pte = false;
bool exec_fault;
bool device = false;
- bool shared;
unsigned long mmu_seq;
struct kvm *kvm = vcpu->kvm;
struct kvm_mmu_memory_cache *memcache = &vcpu->arch.mmu_page_cache;
@@ -1142,8 +1130,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
vma_shift = get_vma_page_shift(vma, hva);
}

- shared = (vma->vm_flags & VM_SHARED);
-
switch (vma_shift) {
#ifndef __PAGETABLE_PMD_FOLDED
case PUD_SHIFT:
@@ -1264,12 +1250,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,

if (fault_status != FSC_PERM && !device && kvm_has_mte(kvm)) {
/* Check the VMM hasn't introduced a new VM_SHARED VMA */
- if (!shared)
- ret = sanitise_mte_tags(kvm, pfn, vma_pagesize);
- else
+ if ((vma->vm_flags & VM_MTE_ALLOWED) &&
+ !(vma->vm_flags & VM_SHARED)) {
+ sanitise_mte_tags(kvm, pfn, vma_pagesize);
+ } else {
ret = -EFAULT;
- if (ret)
goto out_unlock;
+ }
}

if (writable)
@@ -1491,15 +1478,18 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
kvm_pfn_t pfn = pte_pfn(range->pte);
- int ret;

if (!kvm->arch.mmu.pgt)
return false;

WARN_ON(range->end - range->start != 1);

- ret = sanitise_mte_tags(kvm, pfn, PAGE_SIZE);
- if (ret)
+ /*
+ * If the page isn't tagged, defer to user_mem_abort() for sanitising
+ * the MTE tags. The S2 pte should have been unmapped by
+ * mmu_notifier_invalidate_range_end().
+ */
+ if (kvm_has_mte(kvm) && !page_mte_tagged(pfn_to_page(pfn)))
return false;

/*
--
2.37.1.359.gd136c6c3e2-goog