From db590f2a02907a6762edd0877b32e79405ed4932 Mon Sep 17 00:00:00 2001

From: Peter Xu <peterx@redhat.com>

Date: Mon, 3 Sep 2018 04:52:33 +0200

Subject: [PATCH 18/29] intel-iommu: send PSI always even if across PDEs

RH-Author: Peter Xu <peterx@redhat.com>

Message-id: <20180903045241.6456-2-peterx@redhat.com>

Patchwork-id: 82021

O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 1/9] intel-iommu: send PSI always even if across PDEs

Bugzilla: 1623859

RH-Acked-by: Xiao Wang <jasowang@redhat.com>

RH-Acked-by: Auger Eric <eric.auger@redhat.com>

RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>

SECURITY IMPLICATION: without this patch, any guest with both assigned

device and a vIOMMU might encounter stale IO page mappings even if guest

has already unmapped the page, which may lead to guest memory

corruption.  The stale mappings will only be limited to the guest's own

memory range, so it should not affect the host memory or other guests on

the host.

During IOVA page table walking, there is a special case when the PSI

covers one whole PDE (Page Directory Entry, which contains 512 Page

Table Entries) or more.  In the past, we skip that entry and we don't

notify the IOMMU notifiers.  This is not correct.  We should send UNMAP

notification to registered UNMAP notifiers in this case.

For UNMAP only notifiers, this might cause IOTLBs cached in the devices

even if they were already invalid.  For MAP/UNMAP notifiers like

vfio-pci, this will cause stale page mappings.

This special case doesn't trigger often, but it is very easy to be

triggered by nested device assignments, since in that case we'll

possibly map the whole L2 guest RAM region into the device's IOVA

address space (several GBs at least), which is far bigger than normal

kernel driver usages of the device (tens of MBs normally).

Without this patch applied to L1 QEMU, nested device assignment to L2

guests will dump some errors like:

qemu-system-x86_64: VFIO_MAP_DMA: -17

qemu-system-x86_64: vfio_dma_map(0x557305420c30, 0xad000, 0x1000,

                    0x7f89a920d000) = -17 (File exists)

CC: QEMU Stable <qemu-stable@nongnu.org>

Acked-by: Jason Wang <jasowang@redhat.com>

[peterx: rewrite the commit message]

Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

(cherry picked from commit 36d2d52bdb45f5b753a61fdaf0fe7891f1f5b61d)

Signed-off-by: Peter Xu <peterx@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 hw/i386/intel_iommu.c | 42 ++++++++++++++++++++++++++++++------------

 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c

index fb31de9..b359efd 100644

--- a/hw/i386/intel_iommu.c

+++ b/hw/i386/intel_iommu.c

@@ -722,6 +722,15 @@ static int vtd_iova_to_slpte(VTDContextEntry *ce, uint64_t iova, bool is_write,

 typedef int (*vtd_page_walk_hook)(IOMMUTLBEntry *entry, void *private);

+static int vtd_page_walk_one(IOMMUTLBEntry *entry, int level,

+                             vtd_page_walk_hook hook_fn, void *private)

+{

+    assert(hook_fn);

+    trace_vtd_page_walk_one(level, entry->iova, entry->translated_addr,

+                            entry->addr_mask, entry->perm);

+    return hook_fn(entry, private);

+}

+

 /**

  * vtd_page_walk_level - walk over specific level for IOVA range

  *

@@ -781,28 +790,37 @@ static int vtd_page_walk_level(dma_addr_t addr, uint64_t start,

          */

         entry_valid = read_cur | write_cur;

+        entry.target_as = &address_space_memory;

+        entry.iova = iova & subpage_mask;

+        entry.perm = IOMMU_ACCESS_FLAG(read_cur, write_cur);

+        entry.addr_mask = ~subpage_mask;

+

         if (vtd_is_last_slpte(slpte, level)) {

-            entry.target_as = &address_space_memory;

-            entry.iova = iova & subpage_mask;

             /* NOTE: this is only meaningful if entry_valid == true */

             entry.translated_addr = vtd_get_slpte_addr(slpte, aw);

-            entry.addr_mask = ~subpage_mask;

-            entry.perm = IOMMU_ACCESS_FLAG(read_cur, write_cur);

             if (!entry_valid && !notify_unmap) {

                 trace_vtd_page_walk_skip_perm(iova, iova_next);

                 goto next;

             }

-            trace_vtd_page_walk_one(level, entry.iova, entry.translated_addr,

-                                    entry.addr_mask, entry.perm);

-            if (hook_fn) {

-                ret = hook_fn(&entry, private);

-                if (ret < 0) {

-                    return ret;

-                }

+            ret = vtd_page_walk_one(&entry, level, hook_fn, private);

+            if (ret < 0) {

+                return ret;

             }

         } else {

             if (!entry_valid) {

-                trace_vtd_page_walk_skip_perm(iova, iova_next);

+                if (notify_unmap) {

+                    /*

+                     * The whole entry is invalid; unmap it all.

+                     * Translated address is meaningless, zero it.

+                     */

+                    entry.translated_addr = 0x0;

+                    ret = vtd_page_walk_one(&entry, level, hook_fn, private);

+                    if (ret < 0) {

+                        return ret;

+                    }

+                } else {

+                    trace_vtd_page_walk_skip_perm(iova, iova_next);

+                }

                 goto next;

             }

             ret = vtd_page_walk_level(vtd_get_slpte_addr(slpte, aw), iova,

-- 

1.8.3.1