On 06/29/15 10:03, Paul Durrant wrote:
-----Original Message-----
From: Paul Durrant
Sent: 29 June 2015 13:54
To: Paul Durrant; Don Slutz; xen-devel@lists.xen.org; Jan Beulich
Subject: RE: [Xen-devel] Migration bug added by commit
2df1aa01bef7366798248ac6d03cfb42048b003d
-----Original Message-----
From: xen-devel-boun...@lists.xen.org [mailto:xen-devel-
boun...@lists.xen.org] On Behalf Of Paul Durrant
Sent: 29 June 2015 10:42
To: Don Slutz; xen-devel@lists.xen.org; Jan Beulich
Subject: Re: [Xen-devel] Migration bug added by commit
2df1aa01bef7366798248ac6d03cfb42048b003d
-----Original Message-----
From: Don Slutz [mailto:don.sl...@gmail.com]
Sent: 27 June 2015 22:02
To: xen-devel@lists.xen.org; Paul Durrant; Jan Beulich
Subject: Migration bug added by commit
2df1aa01bef7366798248ac6d03cfb42048b003d
commit 2df1aa01bef7366798248ac6d03cfb42048b003d
Author: Paul Durrant <paul.durr...@citrix.com>
Date: Tue Jun 23 18:07:49 2015 +0200
x86/hvm: remove hvm_io_pending() check in hvmemul_do_io()
...
- rc = X86EMUL_RETRY;
- if ( !hvm_send_assist_req(s, &p) )
+ rc = hvm_send_assist_req(s, &p);
+ if ( rc != X86EMUL_RETRY )
...
if ( unlikely(!vcpu_start_shutdown_deferral(curr)) )
- return 0; /* implicitly bins the i/o operation */
+ return X86EMUL_OKAY;
So now X86EMUL_OKAY is returned from hvmemul_do_io() during
shutdown.
From Jan Beulich about this:
Re: [Xen-devel] [PATCH 3/5] hvmemul_do_io: If the send to the ioreq
server failed do not retry.
<https://www.mail-archive.com/search?l=xen-
de...@lists.xen.org&q=subject:%22Re%5C%3A+%5C%5BXen%5C-
devel%5C%5D+%5C%5BPATCH+3%5C%2F5%5C%5D+hvmemul_do_io%5C%3
A+If+the+send+to+the+ioreq+server+failed+do+not+retry.%22&o=newest
Jan Beulich
<https://www.mail-archive.com/search?l=xen-
de...@lists.xen.org&q=from:%22Jan+Beulich%22>
Fri, 30 Jan 2015 02:24:55 -0800
<https://www.mail-archive.com/search?l=xen-
de...@lists.xen.org&q=date:20150130>
On 30.01.15 at 01:52, <dsl...@verizon.com> wrote:
I.E. do just what no backing DM does.
_If_ this is correct, the if() modified here should be folded with the
one a few lines up. But looking at the description of the commit that
introduced this (bac0999325 "x86 hvm: Do not incorrectly retire an
instruction emulation...", almost immediately modified by f20f3c8ece
"x86 hvm: On failed hvm_send_assist_req(), io emulation...") I doubt
this is really what we want, or at the very least your change
description should explain what was wrong with the original commit.
Jan
going up the call stack:
in handle_pio when hvmemul_do_pio_buffer() returns X86EMUL_OKAY,
it
returns 1.
svm_vmexit_handler 2578 if ( handle_pio(port, bytes, dir) )
or
vmx_vmexit_handler 3178 if ( handle_pio(port, bytes, dir) )
both update the IP in this case which is wrong during shutdown.
If this is indeed the problem then it seems to me that the correct fix is to
add
a check in handle_pio() and return 0 if the cpu is shutting down.
Actually, with some more thought, it sounds like we essentially want to
unwind the I/O emulation if we're shutting down and I think this could be
achieved by having hvm_send_assist_req() return X86EMUL_RETRY if it hits
the shutdown deferral case, having hvm_emul_do_io() reset the emulation
state back to 'none' if the domain is shutting down, and then having
handle_pio() return 0 if sees X86EMUL_RETRY without any form of
completion being requested.
I think this patch should do it for now:
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index a4d7225..cc6130c 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 )
I do not know enough about "is_shutting_down" to agree. What is clear
is that
this test is not the same as "!vcpu_start_shutdown_deferral(curr)".
-Don Slutz
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 8226d8c..aba4ef6 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2547,7 +2547,7 @@ 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;
list_for_each_entry ( sv,
&s->ioreq_vcpu_list,
Paul
Paul
So I think:
rc = hvm_send_assist_req(s, &p);
if ( rc != X86EMUL_RETRY )
vio->io_state = HVMIO_none;
needs to change to:
rc = hvm_send_assist_req(s, &p);
if ( rc != X86EMUL_RETRY )
{
vio->io_state = HVMIO_none;
if ( rc == X86EMUL_OKAY )
rc = X86EMUL_RETRY;
}
-Don Slutz
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