On Mon, 31 Oct 2022 at 10:30, Alex Williamson
<alex.william...@redhat.com> wrote:
>
> On Mon, 31 Oct 2022 09:56:04 +0800
> Cindy Lu <l...@redhat.com> wrote:
>
> > - Move the implement vfio_get_xlat_addr to softmmu/memory.c, and
> > change the name to memory_get_xlat_addr(). So we can use this
> > function on other devices, such as vDPA device.
> > - Add a new function vfio_get_xlat_addr in vfio/common.c, and it will check
> > whether the memory is backed by a discard manager. the device can
> > have its own warning.
> >
> > Signed-off-by: Cindy Lu <l...@redhat.com>
> > ---
> > hw/vfio/common.c | 101 +++++++++++-------------------------------
> > include/exec/memory.h | 4 ++
> > softmmu/memory.c | 72 ++++++++++++++++++++++++++++++
> > 3 files changed, 102 insertions(+), 75 deletions(-)
>
> Some changes I'd like to see below, but otherwise
>
> Acked-by: Alex Williamson <alex.william...@redhat.com>
>
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index ace9562a9b..5bfd55de86 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -578,86 +578,37 @@ static bool
> > vfio_listener_skipped_section(MemoryRegionSection *section)
> > static bool vfio_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> > ram_addr_t *ram_addr, bool *read_only)
> > {
> > - MemoryRegion *mr;
> > - hwaddr xlat;
> > - hwaddr len = iotlb->addr_mask + 1;
> > - bool writable = iotlb->perm & IOMMU_WO;
> > -
> > - /*
> > - * The IOMMU TLB entry we have just covers translation through
> > - * this IOMMU to its immediate target. We need to translate
> > - * it the rest of the way through to memory.
> > - */
> > - mr = address_space_translate(&address_space_memory,
> > - iotlb->translated_addr,
> > - &xlat, &len, writable,
> > - MEMTXATTRS_UNSPECIFIED);
> > - if (!memory_region_is_ram(mr)) {
> > - error_report("iommu map to non memory area %"HWADDR_PRIx"",
> > - xlat);
> > - return false;
> > - } else if (memory_region_has_ram_discard_manager(mr)) {
> > - RamDiscardManager *rdm = memory_region_get_ram_discard_manager(mr);
> > - MemoryRegionSection tmp = {
> > - .mr = mr,
> > - .offset_within_region = xlat,
> > - .size = int128_make64(len),
> > - };
> > -
> > + bool mr_has_discard_manager;
> > + if (memory_get_xlat_addr(iotlb, vaddr, ram_addr, read_only,
> > + &mr_has_discard_manager)) {
> > /*
> > - * Malicious VMs can map memory into the IOMMU, which is expected
> > - * to remain discarded. vfio will pin all pages, populating memory.
> > - * Disallow that. vmstate priorities make sure any
> > RamDiscardManager
> > - * were already restored before IOMMUs are restored.
> > + * if the mr has the discard_manager and the return value of
> > + * memory_get_xlat_addr() is ture then we need to warn
>
> s/ture/true/
>
> But then the comment below is really describing why we're generating a
> warning, so the above additional comment is mostly just noise.
>
sure, will remove this
> I'd also prefer to see this as:
>
> {
> bool ret, mr_has_discard_manager;
>
> ret = memory_get_xlat_addr(iotlb, vaddr, ram_addr, read_only,
> &mr_has_discard_manager));
>
> if (ret && mr_has_discard_manager) {
> // Unmodified comment and warn report from existing code
> }
>
> return ret;
> }
>
sure, Will change this, Thanks Alex
Thanks
Cindy
> > */
> > - if (!ram_discard_manager_is_populated(rdm, &tmp)) {
> > - error_report("iommu map to discarded memory (e.g., unplugged
> > via"
> > - " virtio-mem): %"HWADDR_PRIx"",
> > - iotlb->translated_addr);
> > - return false;
> > + if (mr_has_discard_manager) {
> > + /*
> > + * Malicious VMs might trigger discarding of IOMMU-mapped
> > memory.
> > + * The pages will remain pinned inside vfio until unmapped,
> > + * resulting in a higher memory consumption than expected. If
> > memory
> > + * would get populated again later, there would be an
> > inconsistency
> > + * between pages pinned by vfio and pages seen by QEMU. This
> > is the
> > + * case until unmapped from the IOMMU (e.g., during device
> > reset).
> > + *
> > + * With malicious guests, we really only care about pinning
> > more
> > + * memory than expected. RLIMIT_MEMLOCK set for the
> > user/process can
> > + * never be exceeded and can be used to mitigate this problem.
> > + */
> > + warn_report_once(
> > + "Using vfio with vIOMMUs and coordinated discarding of"
> > + " RAM (e.g., virtio-mem) works, however, malicious"
> > + " guests can trigger pinning of more memory than"
> > + " intended via an IOMMU. It's possible to mitigate "
> > + " by setting/adjusting RLIMIT_MEMLOCK.");
> > }
> >
> > - /*
> > - * Malicious VMs might trigger discarding of IOMMU-mapped memory.
> > The
> > - * pages will remain pinned inside vfio until unmapped, resulting
> > in a
> > - * higher memory consumption than expected. If memory would get
> > - * populated again later, there would be an inconsistency between
> > pages
> > - * pinned by vfio and pages seen by QEMU. This is the case until
> > - * unmapped from the IOMMU (e.g., during device reset).
> > - *
> > - * With malicious guests, we really only care about pinning more
> > memory
> > - * than expected. RLIMIT_MEMLOCK set for the user/process can
> > never be
> > - * exceeded and can be used to mitigate this problem.
> > - */
> > - warn_report_once("Using vfio with vIOMMUs and coordinated
> > discarding of"
> > - " RAM (e.g., virtio-mem) works, however,
> > malicious"
> > - " guests can trigger pinning of more memory than"
> > - " intended via an IOMMU. It's possible to
> > mitigate "
> > - " by setting/adjusting RLIMIT_MEMLOCK.");
> > - }
> > -
> > - /*
> > - * Translation truncates length to the IOMMU page size,
> > - * check that it did not truncate too much.
> > - */
> > - if (len & iotlb->addr_mask) {
> > - error_report("iommu has granularity incompatible with target AS");
> > - return false;
> > - }
> > -
> > - if (vaddr) {
> > - *vaddr = memory_region_get_ram_ptr(mr) + xlat;
> > + return true;
> > }
> > -
> > - if (ram_addr) {
> > - *ram_addr = memory_region_get_ram_addr(mr) + xlat;
> > - }
> > -
> > - if (read_only) {
> > - *read_only = !writable || mr->readonly;
> > - }
> > -
> > - return true;
> > + return false;
> > }
> >
> > static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> > diff --git a/include/exec/memory.h b/include/exec/memory.h
> > index bfb1de8eea..d1e79c39dc 100644
> > --- a/include/exec/memory.h
> > +++ b/include/exec/memory.h
> > @@ -713,6 +713,10 @@ void
> > ram_discard_manager_register_listener(RamDiscardManager *rdm,
> > void ram_discard_manager_unregister_listener(RamDiscardManager *rdm,
> > RamDiscardListener *rdl);
> >
> > +bool memory_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> > + ram_addr_t *ram_addr, bool *read_only,
> > + bool *mr_has_discard_manager);
> > +
> > typedef struct CoalescedMemoryRange CoalescedMemoryRange;
> > typedef struct MemoryRegionIoeventfd MemoryRegionIoeventfd;
> >
> > diff --git a/softmmu/memory.c b/softmmu/memory.c
> > index 7ba2048836..bc0be3f62c 100644
> > --- a/softmmu/memory.c
> > +++ b/softmmu/memory.c
> > @@ -33,6 +33,7 @@
> > #include "qemu/accel.h"
> > #include "hw/boards.h"
> > #include "migration/vmstate.h"
> > +#include "exec/address-spaces.h"
> >
> > //#define DEBUG_UNASSIGNED
> >
> > @@ -2121,6 +2122,77 @@ void
> > ram_discard_manager_unregister_listener(RamDiscardManager *rdm,
> > rdmc->unregister_listener(rdm, rdl);
> > }
> >
> > +/* Called with rcu_read_lock held. */
> > +bool memory_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> > + ram_addr_t *ram_addr, bool *read_only,
> > + bool *mr_has_discard_manager)
> > +{
> > + MemoryRegion *mr;
> > + hwaddr xlat;
> > + hwaddr len = iotlb->addr_mask + 1;
> > + bool writable = iotlb->perm & IOMMU_WO;
> > +
> > + if (mr_has_discard_manager) {
> > + *mr_has_discard_manager = false;
> > + }
> > + /*
> > + * The IOMMU TLB entry we have just covers translation through
> > + * this IOMMU to its immediate target. We need to translate
> > + * it the rest of the way through to memory.
> > + */
> > + mr = address_space_translate(&address_space_memory,
> > iotlb->translated_addr,
> > + &xlat, &len, writable,
> > MEMTXATTRS_UNSPECIFIED);
> > + if (!memory_region_is_ram(mr)) {
> > + error_report("iommu map to non memory area %" HWADDR_PRIx "",
> > xlat);
> > + return false;
> > + } else if (memory_region_has_ram_discard_manager(mr)) {
> > + RamDiscardManager *rdm = memory_region_get_ram_discard_manager(mr);
> > + MemoryRegionSection tmp = {
> > + .mr = mr,
> > + .offset_within_region = xlat,
> > + .size = int128_make64(len),
> > + };
> > + if (mr_has_discard_manager) {
> > + *mr_has_discard_manager = true;
> > + }
> > + /*
> > + * Malicious VMs can map memory into the IOMMU, which is expected
> > + * to remain discarded. vfio will pin all pages, populating memory.
> > + * Disallow that. vmstate priorities make sure any
> > RamDiscardManager
> > + * were already restored before IOMMUs are restored.
> > + */
> > + if (!ram_discard_manager_is_populated(rdm, &tmp)) {
> > + error_report("iommu map to discarded memory (e.g., unplugged
> > via"
> > + " virtio-mem): %" HWADDR_PRIx "",
> > + iotlb->translated_addr);
> > + return false;
> > + }
> > + }
> > +
> > + /*
> > + * Translation truncates length to the IOMMU page size,
> > + * check that it did not truncate too much.
> > + */
> > + if (len & iotlb->addr_mask) {
> > + error_report("iommu has granularity incompatible with target AS");
> > + return false;
> > + }
> > +
> > + if (vaddr) {
> > + *vaddr = memory_region_get_ram_ptr(mr) + xlat;
> > + }
> > +
> > + if (ram_addr) {
> > + *ram_addr = memory_region_get_ram_addr(mr) + xlat;
> > + }
> > +
> > + if (read_only) {
> > + *read_only = !writable || mr->readonly;
> > + }
> > +
> > + return true;
> > +}
> > +
> > void memory_region_set_log(MemoryRegion *mr, bool log, unsigned client)
> > {
> > uint8_t mask = 1 << client;
>
