[PATCH 0/2] Drivers: hv: vmbus: Miscellaneous improvements

[PATCH 0/2] Drivers: hv: vmbus: Miscellaneous improvements

[Andrea Parri]

Hi all,

The patchset:

- simplifies/refactors the VMBus negotiation code by introducing
  the table of VMBus protocol versions (patch 1/2),

- enables VMBus protocol versions 5.1 and 5.2 (patch 2/2).

Thanks,
  Andrea

Andrea Parri (2):
  Drivers: hv: vmbus: Introduce table of VMBus protocol versions
  Drivers: hv: vmbus: Enable VMBus protocol versions 5.1 and 5.2

 drivers/hv/connection.c | 63 +++++++++++++++++------------------------
 include/linux/hyperv.h  |  6 ++--
 2 files changed, 30 insertions(+), 39 deletions(-)

-- 
2.23.0

[PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Andrea Parri]

The technique used to get the next VMBus version seems increasisly
clumsy as the number of VMBus versions increases.  Performance is
not a concern since this is only done once during system boot; it's
just that we'll end up with more lines of code than is really needed.

As an alternative, introduce a table with the version numbers listed
in order (from the most recent to the oldest).  vmbus_connect() loops
through the versions listed in the table until it gets an accepted
connection or gets to the end of the table (invalid version).

Suggested-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
 drivers/hv/connection.c | 51 +++++++++++++++--------------------------
 include/linux/hyperv.h  |  2 --
 2 files changed, 19 insertions(+), 34 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 6e4c015783ffc..90a32c9d79403 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -40,29 +40,19 @@ EXPORT_SYMBOL_GPL(vmbus_connection);
 __u32 vmbus_proto_version;
 EXPORT_SYMBOL_GPL(vmbus_proto_version);
 
-static __u32 vmbus_get_next_version(__u32 current_version)
-{
-	switch (current_version) {
-	case (VERSION_WIN7):
-		return VERSION_WS2008;
-
-	case (VERSION_WIN8):
-		return VERSION_WIN7;
-
-	case (VERSION_WIN8_1):
-		return VERSION_WIN8;
-
-	case (VERSION_WIN10):
-		return VERSION_WIN8_1;
-
-	case (VERSION_WIN10_V5):
-		return VERSION_WIN10;
-
-	case (VERSION_WS2008):
-	default:
-		return VERSION_INVAL;
-	}
-}
+/*
+ * Table of VMBus versions listed from newest to oldest; the table
+ * must terminate with VERSION_INVAL.
+ */
+__u32 vmbus_versions[] = {
+	VERSION_WIN10_V5,
+	VERSION_WIN10,
+	VERSION_WIN8_1,
+	VERSION_WIN8,
+	VERSION_WIN7,
+	VERSION_WS2008,
+	VERSION_INVAL
+};
 
 int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
 {
@@ -169,8 +159,8 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
  */
 int vmbus_connect(void)
 {
-	int ret = 0;
 	struct vmbus_channel_msginfo *msginfo = NULL;
+	int i, ret = 0;
 	__u32 version;
 
 	/* Initialize the vmbus connection */
@@ -244,21 +234,18 @@ int vmbus_connect(void)
 	 * version.
 	 */
 
-	version = VERSION_CURRENT;
+	for (i = 0; ; i++) {
+		version = vmbus_versions[i];
+		if (version == VERSION_INVAL)
+			goto cleanup;
 
-	do {
 		ret = vmbus_negotiate_version(msginfo, version);
 		if (ret == -ETIMEDOUT)
 			goto cleanup;
 
 		if (vmbus_connection.conn_state == CONNECTED)
 			break;
-
-		version = vmbus_get_next_version(version);
-	} while (version != VERSION_INVAL);
-
-	if (version == VERSION_INVAL)
-		goto cleanup;
+	}
 
 	vmbus_proto_version = version;
 	pr_info("Vmbus version:%d.%d\n",
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index b4a017093b697..7073f1eb3618c 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -194,8 +194,6 @@ static inline u32 hv_get_avail_to_write_percent(
 
 #define VERSION_INVAL -1
 
-#define VERSION_CURRENT VERSION_WIN10_V5
-
 /* Make maximum size of pipe payload of 16K */
 #define MAX_PIPE_DATA_PAYLOAD		(sizeof(u8) * 16384)
 
-- 
2.23.0

[PATCH 2/2] Drivers: hv: vmbus: Enable VMBus protocol versions 5.1 and 5.2

[Andrea Parri]

Hyper-V has added VMBus protocol versions 5.1 and 5.2 in recent release
versions.  Allow Linux guests to negotiate these new protocol versions
on versions of Hyper-V that support them.

Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
 drivers/hv/connection.c | 12 +++++++-----
 include/linux/hyperv.h  |  4 ++++
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 90a32c9d79403..d05fef3e09080 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -45,6 +45,8 @@ EXPORT_SYMBOL_GPL(vmbus_proto_version);
  * must terminate with VERSION_INVAL.
  */
 __u32 vmbus_versions[] = {
+	VERSION_WIN10_V5_2,
+	VERSION_WIN10_V5_1,
 	VERSION_WIN10_V5,
 	VERSION_WIN10,
 	VERSION_WIN8_1,
@@ -70,12 +72,12 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
 	msg->vmbus_version_requested = version;
 
 	/*
-	 * VMBus protocol 5.0 (VERSION_WIN10_V5) requires that we must use
-	 * VMBUS_MESSAGE_CONNECTION_ID_4 for the Initiate Contact Message,
+	 * VMBus protocol 5.0 (VERSION_WIN10_V5) and higher require that we must
+	 * use VMBUS_MESSAGE_CONNECTION_ID_4 for the Initiate Contact Message,
 	 * and for subsequent messages, we must use the Message Connection ID
 	 * field in the host-returned Version Response Message. And, with
-	 * VERSION_WIN10_V5, we don't use msg->interrupt_page, but we tell
-	 * the host explicitly that we still use VMBUS_MESSAGE_SINT(2) for
+	 * VERSION_WIN10_V5 and higher, we don't use msg->interrupt_page, but we
+	 * tell the host explicitly that we still use VMBUS_MESSAGE_SINT(2) for
 	 * compatibility.
 	 *
 	 * On old hosts, we should always use VMBUS_MESSAGE_CONNECTION_ID (1).
@@ -400,7 +402,7 @@ int vmbus_post_msg(void *buffer, size_t buflen, bool can_sleep)
 		case HV_STATUS_INVALID_CONNECTION_ID:
 			/*
 			 * See vmbus_negotiate_version(): VMBus protocol 5.0
-			 * requires that we must use
+			 * and higher require that we must use
 			 * VMBUS_MESSAGE_CONNECTION_ID_4 for the Initiate
 			 * Contact message, but on old hosts that only
 			 * support VMBus protocol 4.0 or lower, here we get
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 7073f1eb3618c..5ecb2ff7cc25d 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -183,6 +183,8 @@ static inline u32 hv_get_avail_to_write_percent(
  * 3 . 0  (Windows 8 R2)
  * 4 . 0  (Windows 10)
  * 5 . 0  (Newer Windows 10)
+ * 5 . 1  (Windows 10 RS4)
+ * 5 . 2  (Windows Server 2019, RS5)
  */
 
 #define VERSION_WS2008  ((0 << 16) | (13))
@@ -191,6 +193,8 @@ static inline u32 hv_get_avail_to_write_percent(
 #define VERSION_WIN8_1    ((3 << 16) | (0))
 #define VERSION_WIN10	((4 << 16) | (0))
 #define VERSION_WIN10_V5 ((5 << 16) | (0))
+#define VERSION_WIN10_V5_1 ((5 << 16) | (1))
+#define VERSION_WIN10_V5_2 ((5 << 16) | (2))
 
 #define VERSION_INVAL -1
 
-- 
2.23.0

Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Vitaly Kuznetsov]

Andrea Parri <parri.andrea@gmail.com> writes:

> The technique used to get the next VMBus version seems increasisly
> clumsy as the number of VMBus versions increases.  Performance is
> not a concern since this is only done once during system boot; it's
> just that we'll end up with more lines of code than is really needed.
>
> As an alternative, introduce a table with the version numbers listed
> in order (from the most recent to the oldest).  vmbus_connect() loops
> through the versions listed in the table until it gets an accepted
> connection or gets to the end of the table (invalid version).
>
> Suggested-by: Michael Kelley <mikelley@microsoft.com>
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
> ---
>  drivers/hv/connection.c | 51 +++++++++++++++--------------------------
>  include/linux/hyperv.h  |  2 --
>  2 files changed, 19 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 6e4c015783ffc..90a32c9d79403 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -40,29 +40,19 @@ EXPORT_SYMBOL_GPL(vmbus_connection);
>  __u32 vmbus_proto_version;
>  EXPORT_SYMBOL_GPL(vmbus_proto_version);
>  
> -static __u32 vmbus_get_next_version(__u32 current_version)
> -{
> -	switch (current_version) {
> -	case (VERSION_WIN7):
> -		return VERSION_WS2008;
> -
> -	case (VERSION_WIN8):
> -		return VERSION_WIN7;
> -
> -	case (VERSION_WIN8_1):
> -		return VERSION_WIN8;
> -
> -	case (VERSION_WIN10):
> -		return VERSION_WIN8_1;
> -
> -	case (VERSION_WIN10_V5):
> -		return VERSION_WIN10;
> -
> -	case (VERSION_WS2008):
> -	default:
> -		return VERSION_INVAL;
> -	}
> -}
> +/*
> + * Table of VMBus versions listed from newest to oldest; the table
> + * must terminate with VERSION_INVAL.
> + */
> +__u32 vmbus_versions[] = {
> +	VERSION_WIN10_V5,
> +	VERSION_WIN10,
> +	VERSION_WIN8_1,
> +	VERSION_WIN8,
> +	VERSION_WIN7,
> +	VERSION_WS2008,
> +	VERSION_INVAL
> +};
>  
>  int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
>  {
> @@ -169,8 +159,8 @@ int vmbus_negotiate_version(struct vmbus_channel_msginfo *msginfo, u32 version)
>   */
>  int vmbus_connect(void)
>  {
> -	int ret = 0;
>  	struct vmbus_channel_msginfo *msginfo = NULL;
> +	int i, ret = 0;
>  	__u32 version;
>  
>  	/* Initialize the vmbus connection */
> @@ -244,21 +234,18 @@ int vmbus_connect(void)
>  	 * version.
>  	 */
>  
> -	version = VERSION_CURRENT;
> +	for (i = 0; ; i++) {
> +		version = vmbus_versions[i];
> +		if (version == VERSION_INVAL)
> +			goto cleanup;

If you use e.g. ARRAY_SIZE() you can get rid of VERSION_INVAL - and make
this code look more natural.
>  
> -	do {
>  		ret = vmbus_negotiate_version(msginfo, version);
>  		if (ret == -ETIMEDOUT)
>  			goto cleanup;
>  
>  		if (vmbus_connection.conn_state == CONNECTED)
>  			break;
> -
> -		version = vmbus_get_next_version(version);
> -	} while (version != VERSION_INVAL);
> -
> -	if (version == VERSION_INVAL)
> -		goto cleanup;
> +	}
>  
>  	vmbus_proto_version = version;
>  	pr_info("Vmbus version:%d.%d\n",
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index b4a017093b697..7073f1eb3618c 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -194,8 +194,6 @@ static inline u32 hv_get_avail_to_write_percent(
>  
>  #define VERSION_INVAL -1
>  
> -#define VERSION_CURRENT VERSION_WIN10_V5
> -
>  /* Make maximum size of pipe payload of 16K */
>  #define MAX_PIPE_DATA_PAYLOAD		(sizeof(u8) * 16384)

-- 
Vitaly

RE: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Dexuan Cui]

> From: linux-hyperv-owner@vger.kernel.org
> <linux-hyperv-owner@vger.kernel.org> On Behalf Of Andrea Parri
> Sent: Monday, October 7, 2019 9:31 AM
> ....
> +/*
> + * Table of VMBus versions listed from newest to oldest; the table
> + * must terminate with VERSION_INVAL.
> + */
> +__u32 vmbus_versions[] = {
> +	VERSION_WIN10_V5,

This should be "static"?
 
Thanks,
Dexuan

RE: [PATCH 0/2] Drivers: hv: vmbus: Miscellaneous improvements

[Dexuan Cui]

> From: linux-hyperv-owner@vger.kernel.org
> <linux-hyperv-owner@vger.kernel.org> On Behalf Of Andrea Parri
> Sent: Monday, October 7, 2019 9:31 AM
> 
> Hi all,
> 
> The patchset:
> 
> - simplifies/refactors the VMBus negotiation code by introducing
>   the table of VMBus protocol versions (patch 1/2),
> 
> - enables VMBus protocol versions 5.1 and 5.2 (patch 2/2).
> 
> Thanks,
>   Andrea
> 
> Andrea Parri (2):
>   Drivers: hv: vmbus: Introduce table of VMBus protocol versions
>   Drivers: hv: vmbus: Enable VMBus protocol versions 5.1 and 5.2

Should we add a module parameter to allow the user to specify a lower
protocol version, when the VM runs on the latest host? 

This can be useful for testing and debugging purpose: the variable
"vmbus_proto_version" is referenced by the vmbus driver itself and
some VSC drivers: if we always use the latest available proto version,
some code paths can not be tested on the latest hosts. 

Thanks,
-- Dexuan

Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Andrea Parri]

> > @@ -244,21 +234,18 @@ int vmbus_connect(void)
> >  	 * version.
> >  	 */
> >  
> > -	version = VERSION_CURRENT;
> > +	for (i = 0; ; i++) {
> > +		version = vmbus_versions[i];
> > +		if (version == VERSION_INVAL)
> > +			goto cleanup;
> 
> If you use e.g. ARRAY_SIZE() you can get rid of VERSION_INVAL - and make
> this code look more natural.

Thank you for pointing this out, Vitaly.

IIUC, you're suggesting that I do:

	for (i = 0; i < ARRAY_SIZE(vmbus_versions); i++) {
		version = vmbus_versions[i];

		ret = vmbus_negotiate_version(msginfo, version);
		if (ret == -ETIMEDOUT)
			goto cleanup;

		if (vmbus_connection.conn_state == CONNECTED)
			break;
	}

	if (vmbus_connection.conn_state != CONNECTED)
		break;

and that I remove VERSION_INVAL from vmbus_versions, yes?

Looking at the uses of VERSION_INVAL, I find one remaining occurrence
of this macro in vmbus_bus_resume(), which does:

	if (vmbus_proto_version == VERSION_INVAL ||
	    vmbus_proto_version == 0) {
		...
	}

TBH I'm looking at vmbus_bus_resume() and vmbus_bus_suspend() for the
first time and I'm not sure about how to change such check yet... any
suggestions?

Mmh, I see that vmbus_bus_resume() and vmbus_bus_suspend() can access
vmbus_connection.conn_state: can such accesses race with a concurrent
vmbus_connect()?

Thanks,
  Andrea


> >  
> > -	do {
> >  		ret = vmbus_negotiate_version(msginfo, version);
> >  		if (ret == -ETIMEDOUT)
> >  			goto cleanup;
> >  
> >  		if (vmbus_connection.conn_state == CONNECTED)
> >  			break;
> > -
> > -		version = vmbus_get_next_version(version);
> > -	} while (version != VERSION_INVAL);
> > -
> > -	if (version == VERSION_INVAL)
> > -		goto cleanup;
> > +	}
> >  
> >  	vmbus_proto_version = version;
> >  	pr_info("Vmbus version:%d.%d\n",

Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Andrea Parri]

On Mon, Oct 07, 2019 at 05:25:18PM +0000, Dexuan Cui wrote:
> > From: linux-hyperv-owner@vger.kernel.org
> > <linux-hyperv-owner@vger.kernel.org> On Behalf Of Andrea Parri
> > Sent: Monday, October 7, 2019 9:31 AM
> > ....
> > +/*
> > + * Table of VMBus versions listed from newest to oldest; the table
> > + * must terminate with VERSION_INVAL.
> > + */
> > +__u32 vmbus_versions[] = {
> > +	VERSION_WIN10_V5,
> 
> This should be "static"?

I think so, will add in v2.  Thank you for pointing this out, Dexuan.

  Andrea

Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Andrea Parri]

> IIUC, you're suggesting that I do:
> 
> 	for (i = 0; i < ARRAY_SIZE(vmbus_versions); i++) {
> 		version = vmbus_versions[i];
> 
> 		ret = vmbus_negotiate_version(msginfo, version);
> 		if (ret == -ETIMEDOUT)
> 			goto cleanup;
> 
> 		if (vmbus_connection.conn_state == CONNECTED)
> 			break;
> 	}
> 
> 	if (vmbus_connection.conn_state != CONNECTED)
> 		break;

This "break" should have been "goto cleanup".  Sorry.

  Andrea

Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Vitaly Kuznetsov]

Andrea Parri <parri.andrea@gmail.com> writes:

>> > @@ -244,21 +234,18 @@ int vmbus_connect(void)
>> >  	 * version.
>> >  	 */
>> >  
>> > -	version = VERSION_CURRENT;
>> > +	for (i = 0; ; i++) {
>> > +		version = vmbus_versions[i];
>> > +		if (version == VERSION_INVAL)
>> > +			goto cleanup;
>> 
>> If you use e.g. ARRAY_SIZE() you can get rid of VERSION_INVAL - and make
>> this code look more natural.
>
> Thank you for pointing this out, Vitaly.
>
> IIUC, you're suggesting that I do:
>
> 	for (i = 0; i < ARRAY_SIZE(vmbus_versions); i++) {
> 		version = vmbus_versions[i];
>
> 		ret = vmbus_negotiate_version(msginfo, version);
> 		if (ret == -ETIMEDOUT)
> 			goto cleanup;
>
> 		if (vmbus_connection.conn_state == CONNECTED)
> 			break;
> 	}
>
> 	if (vmbus_connection.conn_state != CONNECTED)
> 		break;
>
> and that I remove VERSION_INVAL from vmbus_versions, yes?
>

Yes, something like that.

> Looking at the uses of VERSION_INVAL, I find one remaining occurrence
> of this macro in vmbus_bus_resume(), which does:
>
> 	if (vmbus_proto_version == VERSION_INVAL ||
> 	    vmbus_proto_version == 0) {
> 		...
> 	}
>
> TBH I'm looking at vmbus_bus_resume() and vmbus_bus_suspend() for the
> first time and I'm not sure about how to change such check yet... any
> suggestions?

Hm, I don't think vmbus_proto_version can ever become == VERSION_INVAL
if we rewrite the code the way you suggest, right? So you'll reduce this
to 'if (!vmbus_proto_version)' meaning we haven't negotiated any version
(yet).

>
> Mmh, I see that vmbus_bus_resume() and vmbus_bus_suspend() can access
> vmbus_connection.conn_state: can such accesses race with a concurrent
> vmbus_connect()?

Let's summon Dexuan who's the author! :-) 

>
> Thanks,
>   Andrea
>
>
>> >  
>> > -	do {
>> >  		ret = vmbus_negotiate_version(msginfo, version);
>> >  		if (ret == -ETIMEDOUT)
>> >  			goto cleanup;
>> >  
>> >  		if (vmbus_connection.conn_state == CONNECTED)
>> >  			break;
>> > -
>> > -		version = vmbus_get_next_version(version);
>> > -	} while (version != VERSION_INVAL);
>> > -
>> > -	if (version == VERSION_INVAL)
>> > -		goto cleanup;
>> > +	}
>> >  
>> >  	vmbus_proto_version = version;
>> >  	pr_info("Vmbus version:%d.%d\n",

-- 
Vitaly

Re: [PATCH 0/2] Drivers: hv: vmbus: Miscellaneous improvements

[Andrea Parri]

On Mon, Oct 07, 2019 at 05:41:10PM +0000, Dexuan Cui wrote:
> > From: linux-hyperv-owner@vger.kernel.org
> > <linux-hyperv-owner@vger.kernel.org> On Behalf Of Andrea Parri
> > Sent: Monday, October 7, 2019 9:31 AM
> > 
> > Hi all,
> > 
> > The patchset:
> > 
> > - simplifies/refactors the VMBus negotiation code by introducing
> >   the table of VMBus protocol versions (patch 1/2),
> > 
> > - enables VMBus protocol versions 5.1 and 5.2 (patch 2/2).
> > 
> > Thanks,
> >   Andrea
> > 
> > Andrea Parri (2):
> >   Drivers: hv: vmbus: Introduce table of VMBus protocol versions
> >   Drivers: hv: vmbus: Enable VMBus protocol versions 5.1 and 5.2
> 
> Should we add a module parameter to allow the user to specify a lower
> protocol version, when the VM runs on the latest host? 
> 
> This can be useful for testing and debugging purpose: the variable
> "vmbus_proto_version" is referenced by the vmbus driver itself and
> some VSC drivers: if we always use the latest available proto version,
> some code paths can not be tested on the latest hosts. 

The idea is appealing to me (altough I made no attempt to implement/test
it yet).  What do others think about this?  Maybe can be considered as a
follow-up patch/work to this series?

Thanks,
  Andrea

Re: [PATCH 0/2] Drivers: hv: vmbus: Miscellaneous improvements

[Vitaly Kuznetsov]

Andrea Parri <parri.andrea@gmail.com> writes:

> On Mon, Oct 07, 2019 at 05:41:10PM +0000, Dexuan Cui wrote:
>> > From: linux-hyperv-owner@vger.kernel.org
>> > <linux-hyperv-owner@vger.kernel.org> On Behalf Of Andrea Parri
>> > Sent: Monday, October 7, 2019 9:31 AM
>> > 
>> > Hi all,
>> > 
>> > The patchset:
>> > 
>> > - simplifies/refactors the VMBus negotiation code by introducing
>> >   the table of VMBus protocol versions (patch 1/2),
>> > 
>> > - enables VMBus protocol versions 5.1 and 5.2 (patch 2/2).
>> > 
>> > Thanks,
>> >   Andrea
>> > 
>> > Andrea Parri (2):
>> >   Drivers: hv: vmbus: Introduce table of VMBus protocol versions
>> >   Drivers: hv: vmbus: Enable VMBus protocol versions 5.1 and 5.2
>> 
>> Should we add a module parameter to allow the user to specify a lower
>> protocol version, when the VM runs on the latest host? 
>> 
>> This can be useful for testing and debugging purpose: the variable
>> "vmbus_proto_version" is referenced by the vmbus driver itself and
>> some VSC drivers: if we always use the latest available proto version,
>> some code paths can not be tested on the latest hosts. 
>
> The idea is appealing to me (altough I made no attempt to implement/test
> it yet).  What do others think about this?  Maybe can be considered as a
> follow-up patch/work to this series?

IMO such debug option makes sense, it shouldn be a simple patch so you
may want to squeeze it in this series as it will definitely have code
dependencies.

-- 
Vitaly

RE: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Dexuan Cui]

> From: Vitaly Kuznetsov <vkuznets@redhat.com>
> Sent: Tuesday, October 8, 2019 6:00 AM
>  ...
> > Looking at the uses of VERSION_INVAL, I find one remaining occurrence
> > of this macro in vmbus_bus_resume(), which does:
> >
> > 	if (vmbus_proto_version == VERSION_INVAL ||
> > 	    vmbus_proto_version == 0) {
> > 		...
> > 	}
> >
> > TBH I'm looking at vmbus_bus_resume() and vmbus_bus_suspend() for the
> > first time and I'm not sure about how to change such check yet... any
> > suggestions?
> 
> Hm, I don't think vmbus_proto_version can ever become == VERSION_INVAL
> if we rewrite the code the way you suggest, right? So you'll reduce this
> to 'if (!vmbus_proto_version)' meaning we haven't negotiated any version
> (yet).

Yeah, Vitaly is correct. The check may be a little paranoid as I believe 
"vmbus_proto_version" must be a negotiated value in vmbus_bus_resume()
and vmbus_bus_suspend().  I added the check just in case.

> > Mmh, I see that vmbus_bus_resume() and vmbus_bus_suspend() can access
> > vmbus_connection.conn_state: can such accesses race with a concurrent
> > vmbus_connect()?
> 
> Let's summon Dexuan who's the author! :-)

There should not be an issue:

vmbus_connect() is called in the early subsys_initcall(hv_acpi_init).

vmbus_bus_suspend() is called late in the PM code after the kernel boots up, e.g.
in the hibernation function hibernation_snapshot() -> dpm_suspend(). 

vmbus_bus_resume() is also called later in late_initcall_sync(software_resume).

In the hibernatin process, vmbus_bus_suspend()/resume() can also be called a
few times, and vmbus_bus_resume() calls vmbus_negotiate_version(). As I
checked, there is no issue, either.

Thanks,
Dexuan

Re: [PATCH 1/2] Drivers: hv: vmbus: Introduce table of VMBus protocol versions

[Andrea Parri]

On Tue, Oct 08, 2019 at 10:41:42PM +0000, Dexuan Cui wrote:
> > From: Vitaly Kuznetsov <vkuznets@redhat.com>
> > Sent: Tuesday, October 8, 2019 6:00 AM
> >  ...
> > > Looking at the uses of VERSION_INVAL, I find one remaining occurrence
> > > of this macro in vmbus_bus_resume(), which does:
> > >
> > > 	if (vmbus_proto_version == VERSION_INVAL ||
> > > 	    vmbus_proto_version == 0) {
> > > 		...
> > > 	}
> > >
> > > TBH I'm looking at vmbus_bus_resume() and vmbus_bus_suspend() for the
> > > first time and I'm not sure about how to change such check yet... any
> > > suggestions?
> > 
> > Hm, I don't think vmbus_proto_version can ever become == VERSION_INVAL
> > if we rewrite the code the way you suggest, right? So you'll reduce this
> > to 'if (!vmbus_proto_version)' meaning we haven't negotiated any version
> > (yet).
> 
> Yeah, Vitaly is correct. The check may be a little paranoid as I believe 
> "vmbus_proto_version" must be a negotiated value in vmbus_bus_resume()
> and vmbus_bus_suspend().  I added the check just in case.
> 
> > > Mmh, I see that vmbus_bus_resume() and vmbus_bus_suspend() can access
> > > vmbus_connection.conn_state: can such accesses race with a concurrent
> > > vmbus_connect()?
> > 
> > Let's summon Dexuan who's the author! :-)
> 
> There should not be an issue:
> 
> vmbus_connect() is called in the early subsys_initcall(hv_acpi_init).
> 
> vmbus_bus_suspend() is called late in the PM code after the kernel boots up, e.g.
> in the hibernation function hibernation_snapshot() -> dpm_suspend(). 
> 
> vmbus_bus_resume() is also called later in late_initcall_sync(software_resume).
> 
> In the hibernatin process, vmbus_bus_suspend()/resume() can also be called a
> few times, and vmbus_bus_resume() calls vmbus_negotiate_version(). As I
> checked, there is no issue, either.

Thank you both for these remarks.

So, I'll proceed with the removal of VERSION_INVAL in v2 of this series.

Thanks,
  Andrea