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@amazon.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>
master commit: 5777a3742d88ff1c0ebc626ceb4fd47f9b3dc6d5
master date: 2020-10-20 14:21:32 +0200

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 64508504570b7150c28b231fc760eaf3667c7077..99201ac6154d5aa063522f95a796e8cae4c30563 100644 (file)
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1222,7 +1222,7 @@ void share_xen_page_with_guest(struct page_info *page, struct domain *d,
 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)
 {
@@ -1294,10 +1294,6 @@ 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 4ff24de73d56cc4a3acdadc344a88ea4a3e2128e..5ca5c8c9a27fc0bd395c90deeb63ca443e274953 100644 (file)
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4678,7 +4678,7 @@ 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)
 {
@@ -4765,9 +4765,20 @@ int xenmem_add_to_physmap_one(
         rc = guest_physmap_add_page(d, gpfn, mfn, PAGE_ORDER_4K);
 
  put_both:
-    /* In the XENMAPSPACE_gmfn case, 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 )
+    {
         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 0ae60378f42bf7db60ada974b797db2096ee75fc..a4cf496f248b1c21bac2157bc87fdcabfe202518 100644 (file)
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -811,11 +811,10 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
 {
     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 )
@@ -831,7 +830,10 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
 
 #ifdef CONFIG_HAS_PASSTHROUGH
     if ( need_iommu(d) )
+    {
         this_cpu(iommu_dont_flush_iotlb) = 1;
+        extra.ppage = &pages[0];
+    }
 #endif
 
     while ( xatp->size > done )
@@ -844,8 +846,12 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
         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;
@@ -856,6 +862,7 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
     if ( need_iommu(d) )
     {
         int ret;
+        unsigned int i;
 
         this_cpu(iommu_dont_flush_iotlb) = 0;
 
@@ -863,6 +870,15 @@ int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,
         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;
@@ -876,6 +892,8 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
                                        struct xen_add_to_physmap_batch *xatpb,
                                        unsigned int extent)
 {
+    union add_to_physmap_extra extra = {};
+
     if ( xatpb->size < extent )
         return -EILSEQ;
 
@@ -884,6 +902,19 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
          !guest_handle_subrange_okay(xatpb->errs, extent, xatpb->size - 1) )
         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 > extent )
     {
         xen_ulong_t idx;
@@ -896,8 +927,7 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
                                                extent, 1)) )
             return -EFAULT;
 
-        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, extent, &rc, 1)) )

diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 24654e8e22647226ee5744166063e8b63e0340a1..38002714de10520b9dc38c5375a1a77277c90368 100644 (file)
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -577,8 +577,22 @@ 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);
 
 int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap *xatp,