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authorAxel Rasmussen2021-05-19 13:03:37 -0700
committerPaolo Bonzini2021-05-27 07:45:56 -0400
commit94f3f2b31a8a9e8bd30bf6f4903ff84acc612e0e (patch)
tree15e044c96aecaba47ff54d4373e0846fc6be4923 /tools
parentc9befd5958fdf8913db69049d47b6ac1d970af03 (diff)
KVM: selftests: create alias mappings when using shared memory
When a memory region is added with a src_type specifying that it should use some kind of shared memory, also create an alias mapping to the same underlying physical pages. And, add an API so tests can get access to these alias addresses. Basically, for a guest physical address, let us look up the analogous host *alias* address. In a future commit, we'll modify the demand paging test to take advantage of this to exercise UFFD minor faults. The idea is, we pre-fault the underlying pages *via the alias*. When the *guest* faults, it gets a "minor" fault (PTEs don't exist yet, but a page is already in the page cache). Then, the userfaultfd theads can handle the fault: they could potentially modify the underlying memory *via the alias* if they wanted to, and then they install the PTEs and let the guest carry on via a UFFDIO_CONTINUE ioctl. Reviewed-by: Ben Gardon <bgardon@google.com> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Message-Id: <20210519200339.829146-9-axelrasmussen@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'tools')
-rw-r--r--tools/testing/selftests/kvm/include/kvm_util.h1
-rw-r--r--tools/testing/selftests/kvm/lib/kvm_util.c49
-rw-r--r--tools/testing/selftests/kvm/lib/kvm_util_internal.h2
3 files changed, 52 insertions, 0 deletions
diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 5d9b35d09251..fcd8e3855111 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -147,6 +147,7 @@ void virt_map(struct kvm_vm *vm, uint64_t vaddr, uint64_t paddr,
void *addr_gpa2hva(struct kvm_vm *vm, vm_paddr_t gpa);
void *addr_gva2hva(struct kvm_vm *vm, vm_vaddr_t gva);
vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva);
+void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa);
/*
* Address Guest Virtual to Guest Physical
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index bc50ca6390d3..f62780719176 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -903,6 +903,19 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm,
vm_userspace_mem_region_gpa_insert(&vm->regions.gpa_tree, region);
vm_userspace_mem_region_hva_insert(&vm->regions.hva_tree, region);
hash_add(vm->regions.slot_hash, &region->slot_node, slot);
+
+ /* If shared memory, create an alias. */
+ if (region->fd >= 0) {
+ region->mmap_alias = mmap(NULL, region->mmap_size,
+ PROT_READ | PROT_WRITE,
+ vm_mem_backing_src_alias(src_type)->flag,
+ region->fd, 0);
+ TEST_ASSERT(region->mmap_alias != MAP_FAILED,
+ "mmap of alias failed, errno: %i", errno);
+
+ /* Align host alias address */
+ region->host_alias = align(region->mmap_alias, alignment);
+ }
}
/*
@@ -1334,6 +1347,42 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva)
}
/*
+ * Address VM physical to Host Virtual *alias*.
+ *
+ * Input Args:
+ * vm - Virtual Machine
+ * gpa - VM physical address
+ *
+ * Output Args: None
+ *
+ * Return:
+ * Equivalent address within the host virtual *alias* area, or NULL
+ * (without failing the test) if the guest memory is not shared (so
+ * no alias exists).
+ *
+ * When vm_create() and related functions are called with a shared memory
+ * src_type, we also create a writable, shared alias mapping of the
+ * underlying guest memory. This allows the host to manipulate guest memory
+ * without mapping that memory in the guest's address space. And, for
+ * userfaultfd-based demand paging, we can do so without triggering userfaults.
+ */
+void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa)
+{
+ struct userspace_mem_region *region;
+ uintptr_t offset;
+
+ region = userspace_mem_region_find(vm, gpa, gpa);
+ if (!region)
+ return NULL;
+
+ if (!region->host_alias)
+ return NULL;
+
+ offset = gpa - region->region.guest_phys_addr;
+ return (void *) ((uintptr_t) region->host_alias + offset);
+}
+
+/*
* VM Create IRQ Chip
*
* Input Args:
diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h
index b30e8c7b119b..a03febc24ba6 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h
+++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h
@@ -19,7 +19,9 @@ struct userspace_mem_region {
int fd;
off_t offset;
void *host_mem;
+ void *host_alias;
void *mmap_start;
+ void *mmap_alias;
size_t mmap_size;
struct rb_node gpa_node;
struct rb_node hva_node;