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Re: [Xen-devel] [PATCH v6 1/4] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.
On 9/9/2016 4:09 PM, Jan Beulich wrote:
On 09.09.16 at 07:55, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
On 9/5/2016 9:31 PM, Jan Beulich wrote:
On 02.09.16 at 12:47, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
@@ -178,8 +179,27 @@ static int hvmemul_do_io(
break;
case X86EMUL_UNHANDLEABLE:
{
- struct hvm_ioreq_server *s =
- hvm_select_ioreq_server(curr->domain, &p);
+ struct hvm_ioreq_server *s = NULL;
+ p2m_type_t p2mt = p2m_invalid;
+
+ if ( is_mmio )
+ {
+ unsigned long gmfn = paddr_to_pfn(addr);
+
+ (void) get_gfn_query_unlocked(currd, gmfn, &p2mt);
+
+ if ( p2mt == p2m_ioreq_server && dir == IOREQ_WRITE )
+ {
+ unsigned int flags;
+
+ s = p2m_get_ioreq_server(currd, &flags);
+ if ( !(flags & XEN_HVMOP_IOREQ_MEM_ACCESS_WRITE) )
+ s = NULL;
+ }
+ }
+
+ if ( !s && p2mt != p2m_ioreq_server )
+ s = hvm_select_ioreq_server(currd, &p);
What I recall is that we had agreed on p2m_ioreq_server pages
to be treated as ordinary RAM ones as long as no server can be
found. The type check here contradicts that. Is there a reason?
Thanks Jan. I had given my explaination on Sep 6's reply. :)
If s is NULL for a p2m_ioreq_server page, we do not wish to traverse the
rangeset
by hvm_select_ioreq_server() again, it may probably be a read emulation
process
for a read-modify-write scenario.
Well, yes, I recall. Yet my request stands: At the very least there
should be a comment here outlining the intended behavior. That'll
make it quite a bit easier, I think, for the reader to figure whether
the code actually matches those intentions (and also help people
needing to touch this code again down the road).
OK. Thanks. I'll add a comment here. :)
Yu
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