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Re: [Xen-devel] [For Xen-4.10 RFC PATCH 3/3] Prevent redundant icache flushes in populate_physmap()
Hi Punit,
Sorry for the late answer.
On 31/03/17 11:24, Punit Agrawal wrote:
populate_physmap() calls alloc_heap_pages() per requested extent. As
alloc_heap_pages() performs icache maintenance operations affecting the
entire instruction cache, this leads to redundant cache flushes when
allocating multiple extents in populate_physmap().
To alleviate this problem, introduce a new flag "MEMF_no_icache_flush"
which can be used prevent alloc_heap_pages() to perform unnecessary
icache maintenance operations. Use the flag in populate_physmap() and
perform the required icache maintenance function at the end of the
operation.
Signed-off-by: Punit Agrawal <punit.agrawal@xxxxxxx>
---
xen/common/memory.c | 6 ++++++
xen/common/page_alloc.c | 2 +-
xen/include/asm-x86/page.h | 4 ++++
xen/include/xen/mm.h | 2 ++
4 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/xen/common/memory.c b/xen/common/memory.c
index ad0b33ceb6..507f363924 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -162,6 +162,8 @@ static void populate_physmap(struct memop_args *a)
if ( unlikely(!d->creation_finished) )
a->memflags |= MEMF_no_tlbflush;
+ a->memflags |= MEMF_no_icache_flush;
+
for ( i = a->nr_done; i < a->nr_extents; i++ )
{
if ( i != a->nr_done && hypercall_preempt_check() )
@@ -253,6 +255,10 @@ 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();
I think it would be good to explain why it is always fine to defer the
cache invalidation from a security point of view for future reference.
This would help us in the future to know why we made this choice.
Cheers,
--
Julien Grall
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