[Xen-devel] [For Xen-4.10 PATCH 3/3] Avoid excess icache flushes in populate_physmap() before domain has been created

[Punit Agrawal <punit.agrawal@xxxxxxx>]

populate_physmap() calls alloc_heap_pages() per requested
extent. alloc_heap_pages() invalidates the entire icache per
extent. During domain creation, the icache invalidations can be deffered
until all the extents have been allocated as there is no risk of
executing stale instructions from the icache.

Introduce a new flag "MEMF_no_icache_flush" to be used to prevent
alloc_heap_pages() from performing icache maintenance operations. Use
the flag in populate_physmap() before the domain has been unpaused and
perform required icache maintenance function at the end of the
allocation.

One concern is the lack of synchronisation around testing for
"creation_finished". But it seems, in practice the window where it is
out of sync should be small enough to not matter.

Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
---
 xen/common/memory.c        | 31 ++++++++++++++++++++++---------
 xen/common/page_alloc.c    |  2 +-
 xen/include/asm-x86/page.h |  4 ++++
 xen/include/xen/mm.h       |  2 ++
 4 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 52879e7438..34d2dda8b4 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -152,16 +152,26 @@ static void populate_physmap(struct memop_args *a)
                             max_order(curr_d)) )
         return;
 
-    /*
-     * With MEMF_no_tlbflush set, alloc_heap_pages() will ignore
-     * TLB-flushes. After VM creation, this is a security issue (it can
-     * make pages accessible to guest B, when guest A may still have a
-     * cached mapping to them). So we do this only during domain creation,
-     * when the domain itself has not yet been unpaused for the first
-     * time.
-     */
     if ( unlikely(!d->creation_finished) )
+    {
+        /*
+         * With MEMF_no_tlbflush set, alloc_heap_pages() will ignore
+         * TLB-flushes. After VM creation, this is a security issue (it can
+         * make pages accessible to guest B, when guest A may still have a
+         * cached mapping to them). So we do this only during domain creation,
+         * when the domain itself has not yet been unpaused for the first
+         * time.
+         */
         a->memflags |= MEMF_no_tlbflush;
+        /*
+         * With MEMF_no_icache_flush, alloc_heap_pages() will skip
+         * performing icache flushes. We do it only before domain
+         * creation as once the domain is running there is a danger of
+         * executing instructions from stale caches if icache flush is
+         * delayed.
+         */
+        a->memflags |= MEMF_no_icache_flush;
+    }
 
     for ( i = a->nr_done; i < a->nr_extents; i++ )
     {
@@ -211,7 +221,6 @@ static void populate_physmap(struct memop_args *a)
                 }
 
                 mfn = gpfn;
-                page = mfn_to_page(mfn);
             }
             else
             {
@@ -255,6 +264,10 @@ static void populate_physmap(struct memop_args *a)
 out:
     if ( need_tlbflush )
         filtered_flush_tlb_mask(tlbflush_timestamp);
+
+    if ( a->memflags & MEMF_no_icache_flush )
+        invalidate_icache();
+
     a->nr_done = i;
 }
 
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index eba78f1a3d..8bcef6a547 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -833,7 +833,7 @@ static struct page_info *alloc_heap_pages(
         /* Ensure cache and RAM are consistent for platforms where the
          * guest can control its own visibility of/through the cache.
          */
-        flush_page_to_ram(page_to_mfn(&pg[i]), true);
+        flush_page_to_ram(page_to_mfn(&pg[i]), !(memflags & 
MEMF_no_icache_flush));
     }
 
     spin_unlock(&heap_lock);
diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index 4cadb12646..3a375282f6 100644
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -375,6 +375,10 @@ perms_strictly_increased(uint32_t old_flags, uint32_t 
new_flags)
 
 #define PAGE_ALIGN(x) (((x) + PAGE_SIZE - 1) & PAGE_MASK)
 
+static inline void invalidate_icache(void)
+{
+}
+
 #endif /* __X86_PAGE_H__ */
 
 /*
diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 88de3c1fa6..ee50d4cd7b 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -224,6 +224,8 @@ struct npfec {
 #define  MEMF_no_owner    (1U<<_MEMF_no_owner)
 #define _MEMF_no_tlbflush 6
 #define  MEMF_no_tlbflush (1U<<_MEMF_no_tlbflush)
+#define _MEMF_no_icache_flush 7
+#define  MEMF_no_icache_flush (1U<<_MEMF_no_icache_flush)
 #define _MEMF_node        8
 #define  MEMF_node_mask   ((1U << (8 * sizeof(nodeid_t))) - 1)
 #define  MEMF_node(n)     ((((n) + 1) & MEMF_node_mask) << _MEMF_node)
-- 
2.11.0


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