Re: [PATCH v6 1/2] vfio: move function vfio_get_xlat_addr() to memory.c

[Alex Williamson <alex.williamson@redhat.com>]

On Sun, 30 Oct 2022 14:01:05 +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      | 135 ++++++++++++++----------------------------
>  include/exec/memory.h |   4 ++
>  softmmu/memory.c      |  72 ++++++++++++++++++++++
>  3 files changed, 122 insertions(+), 89 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index ace9562a9b..06ebbb82c7 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -574,92 +574,6 @@ 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)
> -{
> -    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;
> -        }
> -
> -        /*
> -         * 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;
> -    }
> -
> -    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 +595,32 @@ 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 (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.");
> +        }
>          /*
>           * vaddr is only valid until rcu_read_unlock(). But after
>           * vfio_dma_map has set up the mapping the pages will be
> @@ -1349,6 +1285,7 @@ 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 +1296,9 @@ 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 +1307,26 @@ static void vfio_iommu_map_dirty_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
>                           container, iova,
>                           iotlb->addr_mask + 1, ret);
>          }
> +        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.");
> +        }

This still needs a vfio wrapper to avoid the duplicate comment and
warn_report_once.  Thanks,

Alex


>      }
>      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;