On 06/30/15 09:45, Andrew Cooper wrote:
On 30/06/15 14:05, Paul Durrant wrote:
The addition of commit 2df1aa01 "x86/hvm: remove hvm_io_pending() check
in hvmemul_do_io()" causes a problem in migration because I/O that was
caught by the test of vcpu_start_shutdown_deferral() in
hvm_send_assist_req() is now considered completed rather than requiring
a retry.
This patch fixes the problem by having hvm_send_assist_req() return
X86EMUL_RETRY rather than X86EMUL_OKAY if the
vcpu_start_shutdown_deferral() test fails and then making sure that
the emulation state is reset if the domain is found to be shutting
down.
Reported-by: Don Slutz <don.sl...@gmail.com>
Signed-off-by: Paul Durrant <paul.durr...@citrix.com>
Keir Fraser <k...@xen.org>
Jan Beulich <jbeul...@suse.com>
Andrew Cooper <andrew.coop...@citrix.com>
Reviewed-by: Andrew Cooper <andrew.coop...@citrix.com>
---
xen/arch/x86/hvm/emulate.c | 2 +-
xen/arch/x86/hvm/hvm.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index fe5661d..8b60843 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -183,7 +183,7 @@ static int hvmemul_do_io(
else
{
rc = hvm_send_assist_req(s, &p);
- if ( rc != X86EMUL_RETRY )
+ if ( rc != X86EMUL_RETRY || curr->domain->is_shutting_down )
Having spent more time thinking about this, a safer test is "!curr->
defer_shutdown" .
The reason are as follows:
1) This uses what vcpu_start_shutdown_deferral() returns. But it is
only valid if
vcpu_start_shutdown_deferral() is called which is the case now.
2) The checking of "curr->domain->is_shutting_down" without also
checking for "curr-> defer_shutdown" may open a timing window.
3) No use of "spin_lock(&d->shutdown_lock)".
vio->io_state = HVMIO_none;
else if ( data_is_addr || dir == IOREQ_WRITE )
rc = X86EMUL_OKAY;
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 535d622..f0cf064 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2613,7 +2613,7 @@ int hvm_send_assist_req(struct hvm_ioreq_server *s,
ioreq_t *proto_p)
ASSERT(s);
if ( unlikely(!vcpu_start_shutdown_deferral(curr)) )
- return X86EMUL_OKAY;
+ return X86EMUL_RETRY;
I will also note that this change makes hvm_send_assist_req() have only
2 return codes:
X86EMUL_RETRY
X86EMUL_UNHANDLEABLE
and so is not clear why its return should not be a bool.
And there are now 2 reasons why X86EMUL_RETRY is returned, which require
the caller to redo a test.
Granted X86EMUL_OKAY is bad. But I wounder if it would be better to add
an enum for
hvm_send_assist_req() to return in stead of overloading the usage of
X86EMUL_UNHANDLEABLE
and X86EMUL_RETRY with yet more meanings.
-Don Slutz
list_for_each_entry ( sv,
&s->ioreq_vcpu_list,
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