From 94f3f2b31a8a9e8bd30bf6f4903ff84acc612e0e Mon Sep 17 00:00:00 2001 From: Axel Rasmussen Date: Wed, 19 May 2021 13:03:37 -0700 Subject: [PATCH] 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 Signed-off-by: Axel Rasmussen Message-Id: <20210519200339.829146-9-axelrasmussen@google.com> Signed-off-by: Paolo Bonzini --- tools/testing/selftests/kvm/include/kvm_util.h | 1 + tools/testing/selftests/kvm/lib/kvm_util.c | 49 ++++++++++++++++++++++ .../testing/selftests/kvm/lib/kvm_util_internal.h | 2 + 3 files changed, 52 insertions(+) diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h index 5d9b35d..fcd8e38 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 bc50ca6..f627807 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, ®ion->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 b30e8c7..a03febc 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; -- 2.7.4