| Message ID | 20210519200339.829146-9-axelrasmussen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: selftests: exercise userfaultfd minor faults | expand |
On Wed, May 19, 2021 at 1:04 PM Axel Rasmussen <axelrasmussen@google.com> wrote: > > 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> > --- > .../testing/selftests/kvm/include/kvm_util.h | 1 + > tools/testing/selftests/kvm/lib/kvm_util.c | 51 +++++++++++++++++++ > .../selftests/kvm/lib/kvm_util_internal.h | 2 + > 3 files changed, 54 insertions(+) > > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h > index a8f022794ce3..0624f25a6803 100644 > --- a/tools/testing/selftests/kvm/include/kvm_util.h > +++ b/tools/testing/selftests/kvm/include/kvm_util.h > @@ -146,6 +146,7 @@ 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 e4a8d0c43c5e..0b88d1bbc1e0 100644 > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > @@ -811,6 +811,19 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm, > > /* Add to linked-list of memory regions. */ > list_add(®ion->list, &vm->userspace_mem_regions); > + > + /* 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); > + } > } > > /* > @@ -1239,6 +1252,44 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) > return -1; > } > > +/* > + * 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; > + > + list_for_each_entry(region, &vm->userspace_mem_regions, list) { This patch fails to compile on top of with db0670ce3361 ("KVM: selftests: Keep track of memslots more efficiently"). This can be reproduced by checking out kvm/master and running `make -C tools/testing/selftests/kvm`. The following diff fixes the compilation error but I did not have time to test it yet: diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c index c98db1846e1b..28e528c19d28 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util.c +++ b/tools/testing/selftests/kvm/lib/kvm_util.c @@ -1374,19 +1374,17 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa) { struct userspace_mem_region *region; + uintptr_t offset; - list_for_each_entry(region, &vm->userspace_mem_regions, list) { - if (!region->host_alias) - continue; + region = userspace_mem_region_find(vm, gpa, gpa); + if (!region) + return NULL; - if ((gpa >= region->region.guest_phys_addr) - && (gpa <= (region->region.guest_phys_addr - + region->region.memory_size - 1))) - return (void *) ((uintptr_t) region->host_alias - + (gpa - region->region.guest_phys_addr)); - } + if (!region->host_alias) + return NULL; - return NULL; + offset = gpa - region->region.guest_phys_addr; + return (void *) ((uintptr_t) region->host_alias + offset); } /* > + if (!region->host_alias) > + continue; > + > + if ((gpa >= region->region.guest_phys_addr) > + && (gpa <= (region->region.guest_phys_addr > + + region->region.memory_size - 1))) > + return (void *) ((uintptr_t) region->host_alias > + + (gpa - region->region.guest_phys_addr)); > + } > + > + return NULL; > +} > + > /* > * VM Create IRQ Chip > * > diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h > index 91ce1b5d480b..a25af33d4a9c 100644 > --- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h > +++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h > @@ -16,7 +16,9 @@ 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 list_head list; > }; > -- > 2.31.1.751.gd2f1c929bd-goog >
I applied this change on top of kvm/master and tested it, and indeed it compiles and works correctly. Paolo, feel free to take this with a: Reviewed-by: Axel Rasmussen <axelrasmussen@google.com> Or alternatively if you prefer I'm happy to send it as a real git-send-email patch. On Tue, May 25, 2021 at 4:50 PM David Matlack <dmatlack@google.com> wrote: > > On Wed, May 19, 2021 at 1:04 PM Axel Rasmussen <axelrasmussen@google.com> wrote: > > > > 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> > > --- > > .../testing/selftests/kvm/include/kvm_util.h | 1 + > > tools/testing/selftests/kvm/lib/kvm_util.c | 51 +++++++++++++++++++ > > .../selftests/kvm/lib/kvm_util_internal.h | 2 + > > 3 files changed, 54 insertions(+) > > > > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h > > index a8f022794ce3..0624f25a6803 100644 > > --- a/tools/testing/selftests/kvm/include/kvm_util.h > > +++ b/tools/testing/selftests/kvm/include/kvm_util.h > > @@ -146,6 +146,7 @@ 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 e4a8d0c43c5e..0b88d1bbc1e0 100644 > > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > > @@ -811,6 +811,19 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm, > > > > /* Add to linked-list of memory regions. */ > > list_add(®ion->list, &vm->userspace_mem_regions); > > + > > + /* 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); > > + } > > } > > > > /* > > @@ -1239,6 +1252,44 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) > > return -1; > > } > > > > +/* > > + * 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; > > + > > + list_for_each_entry(region, &vm->userspace_mem_regions, list) { > > This patch fails to compile on top of with db0670ce3361 ("KVM: > selftests: Keep track of memslots more efficiently"). > > This can be reproduced by checking out kvm/master and running `make -C > tools/testing/selftests/kvm`. > > The following diff fixes the compilation error but I did not have time > to test it yet: > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c > b/tools/testing/selftests/kvm/lib/kvm_util.c > index c98db1846e1b..28e528c19d28 100644 > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > @@ -1374,19 +1374,17 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) > void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa) > { > struct userspace_mem_region *region; > + uintptr_t offset; > > - list_for_each_entry(region, &vm->userspace_mem_regions, list) { > - if (!region->host_alias) > - continue; > + region = userspace_mem_region_find(vm, gpa, gpa); > + if (!region) > + return NULL; > > - if ((gpa >= region->region.guest_phys_addr) > - && (gpa <= (region->region.guest_phys_addr > - + region->region.memory_size - 1))) > - return (void *) ((uintptr_t) region->host_alias > - + (gpa - region->region.guest_phys_addr)); > - } > + if (!region->host_alias) > + return NULL; > > - return NULL; > + offset = gpa - region->region.guest_phys_addr; > + return (void *) ((uintptr_t) region->host_alias + offset); > } > > /* > > > > > + if (!region->host_alias) > > + continue; > > + > > + if ((gpa >= region->region.guest_phys_addr) > > + && (gpa <= (region->region.guest_phys_addr > > + + region->region.memory_size - 1))) > > + return (void *) ((uintptr_t) region->host_alias > > + + (gpa - region->region.guest_phys_addr)); > > + } > > + > > + return NULL; > > +} > > + > > /* > > * VM Create IRQ Chip > > * > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h > > index 91ce1b5d480b..a25af33d4a9c 100644 > > --- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h > > +++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h > > @@ -16,7 +16,9 @@ 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 list_head list; > > }; > > -- > > 2.31.1.751.gd2f1c929bd-goog > >
On 26/05/21 19:22, Axel Rasmussen wrote: > I applied this change on top of kvm/master and tested it, and indeed > it compiles and works correctly. > > Paolo, feel free to take this with a: > > Reviewed-by: Axel Rasmussen <axelrasmussen@google.com> > > Or alternatively if you prefer I'm happy to send it as a real > git-send-email patch. Yes, I squashed it. Paolo > On Tue, May 25, 2021 at 4:50 PM David Matlack <dmatlack@google.com> wrote: >> >> On Wed, May 19, 2021 at 1:04 PM Axel Rasmussen <axelrasmussen@google.com> wrote: >>> >>> 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> >>> --- >>> .../testing/selftests/kvm/include/kvm_util.h | 1 + >>> tools/testing/selftests/kvm/lib/kvm_util.c | 51 +++++++++++++++++++ >>> .../selftests/kvm/lib/kvm_util_internal.h | 2 + >>> 3 files changed, 54 insertions(+) >>> >>> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h >>> index a8f022794ce3..0624f25a6803 100644 >>> --- a/tools/testing/selftests/kvm/include/kvm_util.h >>> +++ b/tools/testing/selftests/kvm/include/kvm_util.h >>> @@ -146,6 +146,7 @@ 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 e4a8d0c43c5e..0b88d1bbc1e0 100644 >>> --- a/tools/testing/selftests/kvm/lib/kvm_util.c >>> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c >>> @@ -811,6 +811,19 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm, >>> >>> /* Add to linked-list of memory regions. */ >>> list_add(®ion->list, &vm->userspace_mem_regions); >>> + >>> + /* 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); >>> + } >>> } >>> >>> /* >>> @@ -1239,6 +1252,44 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) >>> return -1; >>> } >>> >>> +/* >>> + * 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; >>> + >>> + list_for_each_entry(region, &vm->userspace_mem_regions, list) { >> >> This patch fails to compile on top of with db0670ce3361 ("KVM: >> selftests: Keep track of memslots more efficiently"). >> >> This can be reproduced by checking out kvm/master and running `make -C >> tools/testing/selftests/kvm`. >> >> The following diff fixes the compilation error but I did not have time >> to test it yet: >> >> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c >> b/tools/testing/selftests/kvm/lib/kvm_util.c >> index c98db1846e1b..28e528c19d28 100644 >> --- a/tools/testing/selftests/kvm/lib/kvm_util.c >> +++ b/tools/testing/selftests/kvm/lib/kvm_util.c >> @@ -1374,19 +1374,17 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) >> void *addr_gpa2alias(struct kvm_vm *vm, vm_paddr_t gpa) >> { >> struct userspace_mem_region *region; >> + uintptr_t offset; >> >> - list_for_each_entry(region, &vm->userspace_mem_regions, list) { >> - if (!region->host_alias) >> - continue; >> + region = userspace_mem_region_find(vm, gpa, gpa); >> + if (!region) >> + return NULL; >> >> - if ((gpa >= region->region.guest_phys_addr) >> - && (gpa <= (region->region.guest_phys_addr >> - + region->region.memory_size - 1))) >> - return (void *) ((uintptr_t) region->host_alias >> - + (gpa - region->region.guest_phys_addr)); >> - } >> + if (!region->host_alias) >> + return NULL; >> >> - return NULL; >> + offset = gpa - region->region.guest_phys_addr; >> + return (void *) ((uintptr_t) region->host_alias + offset); >> } >> >> /* >> >> >> >>> + if (!region->host_alias) >>> + continue; >>> + >>> + if ((gpa >= region->region.guest_phys_addr) >>> + && (gpa <= (region->region.guest_phys_addr >>> + + region->region.memory_size - 1))) >>> + return (void *) ((uintptr_t) region->host_alias >>> + + (gpa - region->region.guest_phys_addr)); >>> + } >>> + >>> + return NULL; >>> +} >>> + >>> /* >>> * VM Create IRQ Chip >>> * >>> diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h >>> index 91ce1b5d480b..a25af33d4a9c 100644 >>> --- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h >>> +++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h >>> @@ -16,7 +16,9 @@ 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 list_head list; >>> }; >>> -- >>> 2.31.1.751.gd2f1c929bd-goog >>> >
diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h index a8f022794ce3..0624f25a6803 100644 --- a/tools/testing/selftests/kvm/include/kvm_util.h +++ b/tools/testing/selftests/kvm/include/kvm_util.h @@ -146,6 +146,7 @@ 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 e4a8d0c43c5e..0b88d1bbc1e0 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util.c +++ b/tools/testing/selftests/kvm/lib/kvm_util.c @@ -811,6 +811,19 @@ void vm_userspace_mem_region_add(struct kvm_vm *vm, /* Add to linked-list of memory regions. */ list_add(®ion->list, &vm->userspace_mem_regions); + + /* 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); + } } /* @@ -1239,6 +1252,44 @@ vm_paddr_t addr_hva2gpa(struct kvm_vm *vm, void *hva) return -1; } +/* + * 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; + + list_for_each_entry(region, &vm->userspace_mem_regions, list) { + if (!region->host_alias) + continue; + + if ((gpa >= region->region.guest_phys_addr) + && (gpa <= (region->region.guest_phys_addr + + region->region.memory_size - 1))) + return (void *) ((uintptr_t) region->host_alias + + (gpa - region->region.guest_phys_addr)); + } + + return NULL; +} + /* * VM Create IRQ Chip * diff --git a/tools/testing/selftests/kvm/lib/kvm_util_internal.h b/tools/testing/selftests/kvm/lib/kvm_util_internal.h index 91ce1b5d480b..a25af33d4a9c 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util_internal.h +++ b/tools/testing/selftests/kvm/lib/kvm_util_internal.h @@ -16,7 +16,9 @@ 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 list_head list; };