Re: [PATCH v7 1/2] vfio: move function vfio_get_xlat_addr() to memory.c

[Cindy Lu <lulu@redhat.com>]

On Mon, 31 Oct 2022 at 01:35, Alex Williamson
<alex.williamson@redhat.com> wrote:
>
> On Mon, 31 Oct 2022 00:45:38 +0800
> Cindy Lu <lulu@redhat.com> wrote:
>
> > - Move the function 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 bool arg in this function, which shows whether the memory is
> >   backed by a discard manager. So the device can have its own warning.
> >
> > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > ---
> >  hw/vfio/common.c      | 107 +++++++++++-------------------------------
> >  include/exec/memory.h |   4 ++
> >  softmmu/memory.c      |  72 ++++++++++++++++++++++++++++
> >  3 files changed, 104 insertions(+), 79 deletions(-)
> >
> > diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> > index ace9562a9b..a934262f39 100644
> > --- a/hw/vfio/common.c
> > +++ b/hw/vfio/common.c
> > @@ -573,61 +573,20 @@ static bool vfio_listener_skipped_section(MemoryRegionSection *section)
> >              */
> >             section->offset_within_address_space & (1ULL << 63);
> >  }
> > -
> > -/* Called with rcu_read_lock held.  */
> > -static bool vfio_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> > -                               ram_addr_t *ram_addr, bool *read_only)
> > +static inline void vfio_mr_discard_manager_warn(bool mr_has_discard_manager)
> >  {
> > -    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),
> > -        };
> > -
> > -        /*
> > -         * 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;
> > -        }
> > -
> > +    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).
> > +         * 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.
> > +         * 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"
> > @@ -635,31 +594,7 @@ static bool vfio_get_xlat_addr(IOMMUTLBEntry *iotlb, void **vaddr,
> >                           " 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;
> > -    }
> > -
> > -    if (ram_addr) {
> > -        *ram_addr = memory_region_get_ram_addr(mr) + xlat;
> > -    }
> > -
> > -    if (read_only) {
> > -        *read_only = !writable || mr->readonly;
> > -    }
> > -
> > -    return true;
> >  }
> > -
> >  static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> >  {
> >      VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
> > @@ -681,10 +616,17 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> >
> >      if ((iotlb->perm & IOMMU_RW) != IOMMU_NONE) {
> >          bool read_only;
> > +        bool mr_has_discard_manager;
> >
> > -        if (!vfio_get_xlat_addr(iotlb, &vaddr, NULL, &read_only)) {
> > +        if (!memory_get_xlat_addr(iotlb, &vaddr, NULL, &read_only,
> > +                                  &mr_has_discard_manager)) {
> >              goto out;
> >          }
> > +        /*
> > +         * if the mr has the discard_manager and the return value of
> > +         * memory_get_xlat_addr() is ture then we need to warn
> > +         */
> > +        vfio_mr_discard_manager_warn(mr_has_discard_manager);
>
>
> The wrapper should be around the memory_get_xlat_addr() function, not
> a separate helper whose only purpose is to trigger the error report,
> ie. extract all but the warn_report_once() into a shared
> function, keep vfio_get_xlat_addr().  The vfio call sites should not
> change.  Thanks,
>
> Alex
>
Thanks Alex, I have post a new version as your suggestion
Thanks
cindy
> >          /*
> >           * vaddr is only valid until rcu_read_unlock(). But after
> >           * vfio_dma_map has set up the mapping the pages will be
> > @@ -1349,6 +1291,7 @@ static void vfio_iommu_map_dirty_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> >      VFIOContainer *container = giommu->container;
> >      hwaddr iova = iotlb->iova + giommu->iommu_offset;
> >      ram_addr_t translated_addr;
> > +    bool mr_has_discard_manager;
> >
> >      trace_vfio_iommu_map_dirty_notify(iova, iova + iotlb->addr_mask);
> >
> > @@ -1359,9 +1302,9 @@ static void vfio_iommu_map_dirty_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> >      }
> >
> >      rcu_read_lock();
> > -    if (vfio_get_xlat_addr(iotlb, NULL, &translated_addr, NULL)) {
> > +    if (memory_get_xlat_addr(iotlb, NULL, &translated_addr, NULL,
> > +                             &mr_has_discard_manager)) {
> >          int ret;
> > -
> >          ret = vfio_get_dirty_bitmap(container, iova, iotlb->addr_mask + 1,
> >                                      translated_addr);
> >          if (ret) {
> > @@ -1370,6 +1313,12 @@ static void vfio_iommu_map_dirty_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
> >                           container, iova,
> >                           iotlb->addr_mask + 1, ret);
> >          }
> > +
> > +        /*
> > +         * if the mr has the discard_manager and the return value of
> > +         * memory_get_xlat_addr() is ture then we need to warn
> > +         */
> > +        vfio_mr_discard_manager_warn(mr_has_discard_manager);
> >      }
> >      rcu_read_unlock();
> >  }
> > 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;
>