[PATCH v4 7/8] KVM: arm64: permit all VM_MTE_ALLOWED mappings with MTE enabled

[Peter Collingbourne]

Certain VMMs such as crosvm have features (e.g. sandboxing) that depend
on being able to map guest memory as MAP_SHARED. The current restriction
on sharing MAP_SHARED pages with the guest is preventing the use of
those features with MTE. Now that the races between tasks concurrently
clearing tags on the same page have been fixed, remove this restriction.

Note that this is a relaxation of the ABI.

Signed-off-by: Peter Collingbourne <pcc at google.com>
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
Reviewed-by: Steven Price <steven.price at arm.com>
---
 arch/arm64/kvm/mmu.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index e34fbabd8b93..996ea11fb0e5 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1075,14 +1075,6 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
 
 static bool kvm_vma_mte_allowed(struct vm_area_struct *vma)
 {
-	/*
-	 * VM_SHARED mappings are not allowed with MTE to avoid races
-	 * when updating the PG_mte_tagged page flag, see
-	 * sanitise_mte_tags for more details.
-	 */
-	if (vma->vm_flags & VM_SHARED)
-		return false;
-
 	return vma->vm_flags & VM_MTE_ALLOWED;
 }
 
-- 
2.37.3.968.ga6b4b080e4-goog