[xen stable-4.10] IOMMU: hold page ref until after deferred TLB flush

[patchbot@xxxxxxx]

commit d73e9720545d6acb376bd7c2b1b1d7c92aec6e30
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Oct 20 15:20:54 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 20 15:20:54 2020 +0200

    IOMMU: hold page ref until after deferred TLB flush
    
    When moving around a page via XENMAPSPACE_gmfn_range, deferring the TLB
    flush for the "from" GFN range requires that the page remains allocated
    to the guest until the TLB flush has actually occurred. Otherwise a
    parallel hypercall to remove the page would only flush the TLB for the
    GFN it has been moved to, but not the one is was mapped at originally.
    
    This is part of XSA-346.
    
    Fixes: cf95b2a9fd5a ("iommu: Introduce per cpu flag 
(iommu_dont_flush_iotlb) to avoid unnecessary iotlb... ")
    Reported-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
    master commit: 5777a3742d88ff1c0ebc626ceb4fd47f9b3dc6d5
    master date: 2020-10-20 14:21:32 +0200
---
 xen/arch/arm/mm.c    |  6 +-----
 xen/arch/x86/mm.c    | 15 +++++++++++++--
 xen/common/memory.c  | 43 ++++++++++++++++++++++++++++++++++++-------
 xen/include/xen/mm.h | 16 +++++++++++++++-
 4 files changed, 65 insertions(+), 15 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index cbc0e7c739..7599a32127 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1225,7 +1225,7 @@ void share_xen_page_with_privileged_guests(
 int xenmem_add_to_physmap_one(
     struct domain *d,
     unsigned int space,
-    union xen_add_to_physmap_batch_extra extra,
+    union add_to_physmap_extra extra,
     unsigned long idx,
     gfn_t gfn)
 {
@@ -1297,10 +1297,6 @@ int xenmem_add_to_physmap_one(
         break;
     }
     case XENMAPSPACE_dev_mmio:
-        /* extra should be 0. Reserved for future use. */
-        if ( extra.res0 )
-            return -EOPNOTSUPP;
-
         rc = map_dev_mmio_region(d, gfn, 1, _mfn(idx));
         return rc;
 
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index faa7df30c1..7090be7b4a 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4633,7 +4633,7 @@ static int handle_iomem_range(unsigned long s, unsigned 
long e, void *p)
 int xenmem_add_to_physmap_one(
     struct domain *d,
     unsigned int space,
-    union xen_add_to_physmap_batch_extra extra,
+    union add_to_physmap_extra extra,
     unsigned long idx,
     gfn_t gpfn)
 {
@@ -4723,9 +4723,20 @@ int xenmem_add_to_physmap_one(
         rc = guest_physmap_add_page(d, gpfn, mfn, PAGE_ORDER_4K);
 
  put_both:
-    /* In the XENMAPSPACE_gmfn, we took a ref of the gfn at the top */
+    /*
+     * In the XENMAPSPACE_gmfn case, we took a ref of the gfn at the top.
+     * We also may need to transfer ownership of the page reference to our
+     * caller.
+     */
     if ( space == XENMAPSPACE_gmfn || space == XENMAPSPACE_gmfn_range )
+    {
         put_gfn(d, gfn);
+        if ( !rc && extra.ppage )
+        {
+            *extra.ppage = page;
+            page = NULL;
+        }
+    }
 
     if ( page )
         put_page(page);
diff --git a/xen/common/memory.c b/xen/common/memory.c
index e177941925..08fc9252a3 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -768,11 +768,10 @@ static int xenmem_add_to_physmap(struct domain *d,
 {
     unsigned int done = 0;
     long rc = 0;
-    union xen_add_to_physmap_batch_extra extra;
+    union add_to_physmap_extra extra = {};
+    struct page_info *pages[16];
 
-    if ( xatp->space != XENMAPSPACE_gmfn_foreign )
-        extra.res0 = 0;
-    else
+    if ( xatp->space == XENMAPSPACE_gmfn_foreign )
         extra.foreign_domid = DOMID_INVALID;
 
     if ( xatp->space != XENMAPSPACE_gmfn_range )
@@ -788,7 +787,10 @@ static int xenmem_add_to_physmap(struct domain *d,
 
 #ifdef CONFIG_HAS_PASSTHROUGH
     if ( need_iommu(d) )
+    {
         this_cpu(iommu_dont_flush_iotlb) = 1;
+        extra.ppage = &pages[0];
+    }
 #endif
 
     while ( xatp->size > done )
@@ -801,8 +803,12 @@ static int xenmem_add_to_physmap(struct domain *d,
         xatp->idx++;
         xatp->gpfn++;
 
+        if ( extra.ppage )
+            ++extra.ppage;
+
         /* Check for continuation if it's not the last iteration. */
-        if ( xatp->size > ++done && hypercall_preempt_check() )
+        if ( (++done > ARRAY_SIZE(pages) && extra.ppage) ||
+             (xatp->size > done && hypercall_preempt_check()) )
         {
             rc = start + done;
             break;
@@ -813,6 +819,7 @@ static int xenmem_add_to_physmap(struct domain *d,
     if ( need_iommu(d) )
     {
         int ret;
+        unsigned int i;
 
         this_cpu(iommu_dont_flush_iotlb) = 0;
 
@@ -820,6 +827,15 @@ static int xenmem_add_to_physmap(struct domain *d,
         if ( unlikely(ret) && rc >= 0 )
             rc = ret;
 
+        /*
+         * Now that the IOMMU TLB flush was done for the original GFN, drop
+         * the page references. The 2nd flush below is fine to make later, as
+         * whoever removes the page again from its new GFN will have to do
+         * another flush anyway.
+         */
+        for ( i = 0; i < done; ++i )
+            put_page(pages[i]);
+
         ret = iommu_iotlb_flush(d, xatp->gpfn - done, done);
         if ( unlikely(ret) && rc >= 0 )
             rc = ret;
@@ -835,6 +851,7 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
 {
     unsigned int done = 0;
     int rc;
+    union add_to_physmap_extra extra = {};
 
     if ( xatpb->size < start )
         return -EILSEQ;
@@ -849,6 +866,19 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
          !guest_handle_okay(xatpb->errs, xatpb->size) )
         return -EFAULT;
 
+    switch ( xatpb->space )
+    {
+    case XENMAPSPACE_dev_mmio:
+        /* res0 is reserved for future use. */
+        if ( xatpb->u.res0 )
+            return -EOPNOTSUPP;
+        break;
+
+    case XENMAPSPACE_gmfn_foreign:
+        extra.foreign_domid = xatpb->u.foreign_domid;
+        break;
+    }
+
     while ( xatpb->size > done )
     {
         xen_ulong_t idx;
@@ -866,8 +896,7 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
             goto out;
         }
 
-        rc = xenmem_add_to_physmap_one(d, xatpb->space,
-                                       xatpb->u,
+        rc = xenmem_add_to_physmap_one(d, xatpb->space, extra,
                                        idx, _gfn(gpfn));
 
         if ( unlikely(__copy_to_guest_offset(xatpb->errs, 0, &rc, 1)) )
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index fdcb90841a..4c41e6a69f 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -583,8 +583,22 @@ void scrub_one_page(struct page_info *);
                       &(d)->xenpage_list : &(d)->page_list)
 #endif
 
+union add_to_physmap_extra {
+    /*
+     * XENMAPSPACE_gmfn: When deferring TLB flushes, a page reference needs
+     * to be kept until after the flush, so the page can't get removed from
+     * the domain (and re-used for another purpose) beforehand. By passing
+     * non-NULL, the caller of xenmem_add_to_physmap_one() indicates it wants
+     * to have ownership of such a reference transferred in the success case.
+     */
+    struct page_info **ppage;
+
+    /* XENMAPSPACE_gmfn_foreign */
+    domid_t foreign_domid;
+};
+
 int xenmem_add_to_physmap_one(struct domain *d, unsigned int space,
-                              union xen_add_to_physmap_batch_extra extra,
+                              union add_to_physmap_extra extra,
                               unsigned long idx, gfn_t gfn);
 
 /* Return 0 on success, or negative on error. */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.10