[xen staging] vtd: don't assume addresses are aligned in sync_cache

[patchbot@xxxxxxx]

commit b6d9398144f21718d25daaf8d72669a75592abc5
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Jul 7 14:39:05 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jul 7 14:39:05 2020 +0200

    vtd: don't assume addresses are aligned in sync_cache
    
    Current code in sync_cache assume that the address passed in is
    aligned to a cache line size. Fix the code to support passing in
    arbitrary addresses not necessarily aligned to a cache line size.
    
    This is part of XSA-321.
    
    Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/drivers/passthrough/vtd/iommu.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 93bcd72f84..8a2c105f72 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -149,8 +149,8 @@ static int iommus_incoherent;
 
 static void sync_cache(const void *addr, unsigned int size)
 {
-    int i;
-    static unsigned int clflush_size = 0;
+    static unsigned long clflush_size = 0;
+    const void *end = addr + size;
 
     if ( !iommus_incoherent )
         return;
@@ -158,8 +158,9 @@ static void sync_cache(const void *addr, unsigned int size)
     if ( clflush_size == 0 )
         clflush_size = get_cache_line_size();
 
-    for ( i = 0; i < size; i += clflush_size )
-        cacheline_flush((char *)addr + i);
+    addr -= (unsigned long)addr & (clflush_size - 1);
+    for ( ; addr < end; addr += clflush_size )
+        cacheline_flush((char *)addr);
 }
 
 /* Allocate page table, return its machine address */
--
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