Xen devel - May 2009 - [PATCH] Fix DMA emualtion for ia64.

Hi, Ian and Keir
    In Xen3.4-RC3, we found a regression for creating hvm domains and this issue
is discussed in the thread
http://www.nabble.com/A-strange-issue-when-VTI-guest-vcpus-number-is-near-pcpus-td23400397.html.
This patch is a key fix for Xen-3.4. Without this patch, all hvm guests maybe
crash during booting stage. Could you help to apply it for next release? 
Thanks!
Xiantao

>From 335c33338c5bc315aa2d50b01eeabb7427f4f62c Mon Sep 17 00:00:00 2001
From: Xiantao Zhang <xiantao.zhang@intel.com>
Date: Fri, 8 May 2009 17:06:24 +0800
Subject: [PATCH] Fix DMA emualtion for ia64.
 
For DMA in native system, operating system depends on platform
flushes icache of memory touched by DMA operations.
But as to virtual DMA of virtual machine, dma emulation code has to
use explicit instructions to flush icahce,otherwise,
guest may use old icache and leads to guest''s crash.
 
Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Yang Zhang <yang.zhang@intel.com>
---
 cache-utils.h |   12 ++++++++++++
 cutils.c      |    7 +++++++
 dma-helpers.c |   14 ++++++++++++++
 3 files changed, 33 insertions(+), 0 deletions(-)
 
diff --git a/cache-utils.h b/cache-utils.h
index b45fde4..561d251 100644
--- a/cache-utils.h
+++ b/cache-utils.h
@@ -34,8 +34,20 @@ static inline void flush_icache_range(unsigned long start,
unsigned long stop)
     asm volatile ("isync" : : : "memory");
 }
 
+#elif defined (__ia64__)
+static inline void flush_icache_range(unsigned long start, unsigned long stop)
+{
+    while (start < stop) {
+     asm volatile ("fc %0" :: "r"(start));
+     start += 32;
+    }
+    asm volatile (";;sync.i;;srlz.i;;");
+}
+
+#define qemu_cache_utils_init(envp) do { (void) (envp); } while (0)
 #else
 #define qemu_cache_utils_init(envp) do { (void) (envp); } while (0)
 #endif
 
+
 #endif /* QEMU_CACHE_UTILS_H */
diff --git a/cutils.c b/cutils.c
index 4541214..5137fe1 100644
--- a/cutils.c
+++ b/cutils.c
@@ -23,6 +23,7 @@
  */
 #include "qemu-common.h"
 #include "host-utils.h"
+#include "cache-utils.h"
 
 void pstrcpy(char *buf, size_t buf_size, const char *str)
 {
@@ -157,6 +158,12 @@ void qemu_iovec_from_buffer(QEMUIOVector *qiov, const void
*buf, size_t count)
         if (copy > qiov->iov[i].iov_len)
             copy = qiov->iov[i].iov_len;
         memcpy(qiov->iov[i].iov_base, p, copy);
+
+#ifdef __ia64__
+        flush_icache_range((unsigned long)qiov->iov[i].iov_base,
+                  (unsigned long)(qiov->iov[i].iov_base + copy));
+#endif
+
         p     += copy;
         count -= copy;
     }
diff --git a/dma-helpers.c b/dma-helpers.c
index b2ade19..0523dc8 100644
--- a/dma-helpers.c
+++ b/dma-helpers.c
@@ -9,6 +9,7 @@
 
 #include "dma.h"
 #include "block_int.h"
+#include "cache-utils.h"
 
 void qemu_sglist_init(QEMUSGList *qsg, int alloc_hint)
 {
@@ -135,6 +136,19 @@ static BlockDriverAIOCB *dma_bdrv_io(
     dbs->bh = NULL;
     qemu_iovec_init(&dbs->iov, sg->nsg);
     dma_bdrv_cb(dbs, 0);
+
+#ifdef __ia64__
+    if (!is_write) {
+     int i;
+     QEMUIOVector *qiov;
+        qiov = &dbs->iov;
+        for (i = 0; i < qiov->niov; ++i) {
+           flush_icache_range((unsigned long)qiov->iov[i].iov_base,
+                 (unsigned long)(qiov->iov[i].iov_base +
qiov->iov[i].iov_len));
+ }
+    }
+#endif
+
     return dbs->acb;
 }
 
-- 
1.5.2.4
 
 


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Zhang, Xiantao writes ("[Xen-devel] [PATCH] Fix DMA emualtion for
ia64."):
>     In Xen3.4-RC3, we found a regression for creating hvm domains
> and this issue is discussed in the thread
>
http://www.nabble.com/A-strange-issue-when-VTI-guest-vcpus-number-is-near-pcpus-td23400397.html.
This
> patch is a key fix for Xen-3.4. Without this patch, all hvm guests
> maybe crash during booting stage. Could you help to apply it for
> next release?  Thanks!
Thanks for the report and the patch, which I''m applying.  But I did
have some questions.

These changes are largely to code which we''ve inherited unchanged from
upstream qemu.  Are they specific to Xen ?  I suspect not.  I don''t
really know about the icache coherency rules in ia64 but it seems to
me that if this patch is appropriate for qemu-dm on ia64, it''s
probably also appropriate for kvm-userpace on ia64 (if indeed there is
such a thing) and perhaps also for ordinary translating cpu-emulating
qemu.

In which case perhaps it would be good for us to discuss with qemu
upstream how to address this question.  I don''t think the #ifdef
__ia64__ can be right outside the Xen context; for one thing, we
should use a symbol related to specifically to either the host or the
target architecture (which may be different in qemu of course).  I
assume that the problem exists related to ia64 hosts, rather than ia64
guests ?

Ian.

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Ian Jackson wrote:
> Zhang, Xiantao writes ("[Xen-devel] [PATCH] Fix DMA emualtion for
> ia64."): 
>>     In Xen3.4-RC3, we found a regression for creating hvm domains
>> and this issue is discussed in the thread
>>
http://www.nabble.com/A-strange-issue-when-VTI-guest-vcpus-number-is-near-pcpus-td23400397.html.
>> This patch is a key fix for Xen-3.4. Without this patch, all hvm
>> guests 
>> maybe crash during booting stage. Could you help to apply it for
>> next release?  Thanks!
> 
> Thanks for the report and the patch, which I''m applying.  But I
did
> have some questions.
> 
> These changes are largely to code which we''ve inherited unchanged
from
> upstream qemu.  Are they specific to Xen ?  I suspect not.  I
don''t
> really know about the icache coherency rules in ia64 but it seems to
> me that if this patch is appropriate for qemu-dm on ia64, it''s
> probably also appropriate for kvm-userpace on ia64 (if indeed there is
> such a thing) and perhaps also for ordinary translating cpu-emulating
> qemu.
Yes, it is comment issue for qemu-dm, kvm-userspace and qemu upstream. And we
will push the patch to qemu upstream, and also needs to find a clean solution
for that. As I know, only ia64 platform has such requirement for icache
coherence.

> In which case perhaps it would be good for us to discuss with qemu
> upstream how to address this question.  I don''t think the #ifdef
> __ia64__ can be right outside the Xen context; for one thing, we
> should use a symbol related to specifically to either the host or the
> target architecture (which may be different in qemu of course).  I
> assume that the problem exists related to ia64 hosts, rather than ia64
> guests ?
Since TARGET_IA64 doesn''t work in the context, so I just use __ia64__
instead. As you said, it maybe not proper for all cases of host and guests, but
you know qemu doesn''t work for ia64 regardless of hosts and guests. 
That is to say, Xen or kvm only uses qemu''s device model for virtual
device emualtion, and other parts doesn''t work for them. Certainly, we
should find a clean solution to fix it when we will enable guest and host
support in future.
Xiantao 








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