Hi,
On 12/11/19 4:56 PM, Marc Zyngier wrote:
A device mapping is normally always mapped at Stage-2, since there is very little gain in having it faulted in.
Nonetheless, it is possible to end-up in a situation where the device mapping has been removed from Stage-2 (userspace munmaped the VFIO region, and the MMU notifier did its job), but present in a userspace mapping (userpace has mapped it back at the same address). In such a situation, the device mapping will be demand-paged as the guest performs memory accesses.
This requires to be careful when dealing with mapping size, cache management, and to handle potential execution of a device mapping.
Cc: stable@vger.kernel.org Reported-by: Alexandru Elisei alexandru.elisei@arm.com Signed-off-by: Marc Zyngier maz@kernel.org
virt/kvm/arm/mmu.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index a48994af70b8..0b32a904a1bb 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -38,6 +38,11 @@ static unsigned long io_map_base; #define KVM_S2PTE_FLAG_IS_IOMAP (1UL << 0) #define KVM_S2_FLAG_LOGGING_ACTIVE (1UL << 1) +static bool is_iomap(unsigned long flags) +{
- return flags & KVM_S2PTE_FLAG_IS_IOMAP;
+}
static bool memslot_is_logging(struct kvm_memory_slot *memslot) { return memslot->dirty_bitmap && !(memslot->flags & KVM_MEM_READONLY); @@ -1698,6 +1703,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, vma_pagesize = vma_kernel_pagesize(vma); if (logging_active ||
(vma->vm_flags & VM_PFNMAP) || !fault_supports_stage2_huge_mapping(memslot, hva, vma_pagesize)) {@@ -1760,6 +1766,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, writable = false; }
- if (exec_fault && is_iomap(flags))
return -ENOEXEC;- spin_lock(&kvm->mmu_lock); if (mmu_notifier_retry(kvm, mmu_seq)) goto out_unlock;
@@ -1781,7 +1790,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, if (writable) kvm_set_pfn_dirty(pfn);
- if (fault_status != FSC_PERM)
- if (fault_status != FSC_PERM && !is_iomap(flags)) clean_dcache_guest_page(pfn, vma_pagesize);
if (exec_fault) @@ -1948,9 +1957,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run) if (kvm_is_error_hva(hva) || (write_fault && !writable)) { if (is_iabt) { /* Prefetch Abort on I/O address */
kvm_inject_pabt(vcpu, kvm_vcpu_get_hfar(vcpu));ret = 1;goto out_unlock;
ret = -ENOEXEC;goto out;/* @@ -1992,6 +2000,11 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run) ret = user_mem_abort(vcpu, fault_ipa, memslot, hva, fault_status); if (ret == 0) ret = 1; +out:
- if (ret == -ENOEXEC) {
kvm_inject_pabt(vcpu, kvm_vcpu_get_hfar(vcpu));ret = 1;- }
out_unlock: srcu_read_unlock(&vcpu->kvm->srcu, idx); return ret;
I've tested this patch using the scenario that you described in the commit message. I've also tested it with the following scenarios:
- The region is mmap'ed as backed by a VFIO device fd and the memslot is created, it is munmap'ed, then mmap'ed as anonymous. - The region is mmap'ed as anonymous and the memslot is created, it is munmap'ed, then mmap'ed as backed by a VFIO device fd.
Everything worked as expected, so:
Tested-by: Alexandru Elisei alexandru.elisei@arm.com
Just a nitpick, but stage2_set_pte has a local variable iomap which can be replaced with a call to is_iomap.
Thanks, Alex