From: George Dunlap <george.dunlap@citrix.com>
To: Paul Durrant <Paul.Durrant@citrix.com>,
"Yu, Zhang" <yu.c.zhang@linux.intel.com>,
Jan Beulich <jbeulich@suse.com>, Wei Liu <wei.liu2@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
"Keir (Xen.org)" <keir@xen.org>,
Andrew Cooper <Andrew.Cooper3@citrix.com>,
"Tim (Xen.org)" <tim@xen.org>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
"zhiyuan.lv@intel.com" <zhiyuan.lv@intel.com>,
"jun.nakajima@intel.com" <jun.nakajima@intel.com>
Subject: Re: [PATCH v2 2/3] x86/ioreq server: Rename p2m_mmio_write_dm to p2m_ioreq_server
Date: Thu, 21 Apr 2016 15:09:28 +0100 [thread overview]
Message-ID: <5718DF18.3010405@citrix.com> (raw)
In-Reply-To: <1ba79ba4e2df40b09c40d2f83e12d5c2@AMSPEX02CL03.citrite.net>
On 21/04/16 14:56, Paul Durrant wrote:
>> -----Original Message-----
>> From: Yu, Zhang [mailto:yu.c.zhang@linux.intel.com]
>> Sent: 21 April 2016 14:49
>> To: Paul Durrant; George Dunlap; Jan Beulich; Wei Liu
>> Cc: Kevin Tian; Keir (Xen.org); Andrew Cooper; Tim (Xen.org); xen-
>> devel@lists.xen.org; zhiyuan.lv@intel.com; jun.nakajima@intel.com
>> Subject: Re: [Xen-devel] [PATCH v2 2/3] x86/ioreq server: Rename
>> p2m_mmio_write_dm to p2m_ioreq_server
>>
>>
>>
>> On 4/21/2016 9:31 PM, Paul Durrant wrote:
>>>> -----Original Message-----
>>>> From: Yu, Zhang [mailto:yu.c.zhang@linux.intel.com]
>>>> Sent: 21 April 2016 13:25
>>>> To: George Dunlap; Paul Durrant; Jan Beulich; Wei Liu
>>>> Cc: Kevin Tian; Keir (Xen.org); Andrew Cooper; Tim (Xen.org); xen-
>>>> devel@lists.xen.org; zhiyuan.lv@intel.com; jun.nakajima@intel.com
>>>> Subject: Re: [Xen-devel] [PATCH v2 2/3] x86/ioreq server: Rename
>>>> p2m_mmio_write_dm to p2m_ioreq_server
>>>>
>>>>
>>>>
>>>> On 4/21/2016 1:06 AM, George Dunlap wrote:
>>>>> On 20/04/16 17:58, Paul Durrant wrote:
>>>>>>> -----Original Message-----
>>>>>>> From: Xen-devel [mailto:xen-devel-bounces@lists.xen.org] On Behalf
>>>> Of Jan
>>>>>>> Beulich
>>>>>>> Sent: 20 April 2016 17:53
>>>>>>> To: George Dunlap; Paul Durrant; Wei Liu; yu.c.zhang@linux.intel.com
>>>>>>> Cc: Kevin Tian; Keir (Xen.org); Andrew Cooper; Tim (Xen.org); xen-
>>>>>>> devel@lists.xen.org; zhiyuan.lv@intel.com; jun.nakajima@intel.com
>>>>>>> Subject: Re: [Xen-devel] [PATCH v2 2/3] x86/ioreq server: Rename
>>>>>>> p2m_mmio_write_dm to p2m_ioreq_server
>>>>>>>
>>>>>>>>>> George Dunlap <george.dunlap@citrix.com> 04/20/16 6:30 PM
>>>>>
>>>>>>>> On Wed, Apr 20, 2016 at 4:02 PM, George Dunlap
>>>>>>> <george.dunlap@citrix.com> wrote:
>>>>>>>>> On 19/04/16 12:02, Yu, Zhang wrote:
>>>>>>>>>> So I suppose the only place we need change for this patch is
>>>>>>>>>> for hvmmem_type_t, which should be defined like this?
>>>>>>>>>>
>>>>>>>>>> typedef enum {
>>>>>>>>>> HVMMEM_ram_rw, /* Normal read/write guest RAM */
>>>>>>>>>> HVMMEM_ram_ro, /* Read-only; writes are discarded */
>>>>>>>>>> HVMMEM_mmio_dm, /* Reads and write go to the device
>>>>>>> model */
>>>>>>>>>> #if __XEN_INTERFACE_VERSION__ >= 0x00040700
>>>>>>>>>> HVMMEM_ioreq_server
>>>>>>>>>> #else
>>>>>>>>>> HVMMEM_mmio_write_dm
>>>>>>>>>> #endif
>>>>>>>>>> } hvmmem_type_t;
>>>>>>>>>>
>>>>>>>>>> Besides, does 4.7 still accept freeze exception? It would be great
>>>>>>>>>> if we can get an approval for this.
>>>>>>>>>
>>>>>>>>> Wait, do we *actually* need this? Is anyone actually using this?
>>>>>>>>>
>>>>>>>>> I'd say remove it, and if anyone complains, *then* do the
>> #ifdef'ery
>>>> as
>>>>>>>>> a bug-fix. I'm pretty sure that's Linux's policy -- You Must Keep
>>>>>>>>> Userspace Working, but you can break it to see if anyone complains
>>>> first.
>>>>>>>
>>>>>>> We don't normally do it like that - we aim at keeping things compatible
>>>>>>> right away. I don't know of a case where we would have knowingly
>>>> broken
>>>>>>> compatibility for users of the public headers (leaving aside tool stack
>> only
>>>>>>> stuff of course).
>>>>>>>
>>>>>>>> Going further than this:
>>>>>>>>
>>>>>>>> The proposed patch series not only changes the name, it changes
>> the
>>>>>>>> functionality. We do not want code to *compile* against 4.7 and
>> then
>>>>>>>> not *work* against 4.7; and the worst of all is to compile and sort of
>>>>>>>> work but do it incorrectly.
>>>>>>>
>>>>>>> I had the impression that the renaming patch was what it is - a
>> renaming
>>>>>>> patch, without altering behavior.
>>>>>>>
>>>>>>>> Does the ioreq server have a way of asking Xen what version of the
>> ABI
>>>>>>>> it's providing? I'm assuming the answer is "no"; in which case code
>>>>>>>> that is compiled against the 4.6 interface but run on a 4.8 interface
>>>>>>>> that looks like this will fail in a somewhat unpredictable way.
>>>>>>>
>>>>>>> The only thing it can do is ask for the Xen version. The ABI version is
>> not
>>>>>>> being returned by anything (but perhaps should be).
>>>>>>>
>>>>>>>> Given that:
>>>>>>>>
>>>>>>>> 1. When we do check the ioreq server functionality in, what's the
>>>>>>>> correct way to deal with code that wants to use the old interface,
>> and
>>>>>>>> what do we do with code compiled against the old interface but
>>>> running
>>>>>>>> on the new one?
>>>>>>>
>>>>>>> For the full series I'm not sure I can really tell.But as said, for the
>> rename
>>>>>>> patch alone I thought it is just a rename. And that's what we want to
>> get
>>>>>>> in (see Paul's earlier reply - he wants to see the old name gone, so it
>>>> won't
>>>>>>> be used any further).
>>>>>>>
>>>>>>>> 2. What's the best thing to do for this release?
>>>>>>>
>>>>>>> If the entire series (no matter whether to go in now or later) is
>> changing
>>>>>>> behavior, then the only choice is to consider the currently used enum
>>>>>>> value burnt, and use a fresh one for the new semantics.
>>>>>>
>>>>>> It sounds like that would be best way. If we don't so that then we have
>> to
>>>> maintain the write-dm semantics for pages of that type unless the type is
>>>> claimed (by using the new hypercall) and that's bit icky. I much prefer that
>>>> pages of the new type are treated as RAM until claimed.
>>>>>
>>>>> I think the only sensible way to keep the enum is to also keep the
>>>>> functionality, which would mean using *another* p2m type for
>>>> ioreq_server.
>>>>>
>>>>> Given that the functionality isn't going away for 4.7, I don't see an
>>>>> urgent need to remove the enum; but if Paul does, then a patch
>> renaming
>>>>> it to HVMMEM_unused would be the way forward then I guess. Once
>> the
>>>>> underlying p2m type goes away, you'll want to return -EINVAL for this
>>>>> enum value.
>>>>>
>>>>
>>>> So the enum would be sth. like this?
>>>>
>>>> typedef enum {
>>>> HVMMEM_ram_rw, /* Normal read/write guest RAM */
>>>> HVMMEM_ram_ro, /* Read-only; writes are discarded */
>>>> HVMMEM_mmio_dm, /* Reads and write go to the device model */
>>>> #if __XEN_INTERFACE_VERSION__ < 0x00040700
>>>> HVMMEM_mmio_write_dm, /* Read-only; writes go to the device
>> model
>>>> */
>>>> #else
>>>> HVMMEM_unused,
>>>> #endif
>>>> HVMMEM_ioreq_server
>>>> } hvmmem_type_t;
>>>>
>>>
>>> I believe that's correct, but presumably there's need to be a change to the
>> hypervisor since any reference there to HVMMEM_mmio_write_dm (which I
>> think is limited to the get and set mem type code in hvm.c) will now need to
>> map HVMMEM_unused to the old p2m_mmio_write_dm type.
>>>
>> Thank you, Paul.
>>
>> But p2m_mmio_write_dm will not exist any more...
>> E.g. if in hvmop_get_mem_type(), if type 0xf(p2m_ioreq_server) is
>> returned, we could just return HVMMEM_ioreq_server. No need to
>> worry about the HVMMEM_mmio_write_dm.
>>
>> Maybe we only need to change the beginning of hvmop_set_mem_type()
>> to sth. like this:
>>
>> /* Interface types to internal p2m types */
>> static const p2m_type_t memtype[] = {
>> [HVMMEM_ram_rw] = p2m_ram_rw,
>> [HVMMEM_ram_ro] = p2m_ram_ro,
>> [HVMMEM_mmio_dm] = p2m_mmio_dm,
>> [HVMMEM_unused] = p2m_invalid, /* this will be rejected later */
>> [HVMMEM_ioreq_server] = p2m_ioreq_server
>> };
>> and later in the same routine, just reject the HVMMEM_unused type, in
>> an if(with unlikely) statement.
>>
>
> As long as everyone is in agreement then we can break the functionality that exists in 4.6.1 (and presumably 4.7 now) then that’s ok.
I think we're all in agreement that we can *remove* functionality as
long as (from Xen's perspective) it should fail gracefully. Which means
that if anyone uses the hvm_mem_type enum value previously allocated do
HVMMEM_mmio_write_dm, return an error (one way or another).
The exact method for doing so is up for review.
-George
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next prev parent reply other threads:[~2016-04-21 14:09 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-31 10:53 [PATCH v2 0/3] x86/ioreq server: introduce HVMMEM_ioreq_server mem type Yu Zhang
2016-03-31 10:53 ` [PATCH v2 1/3] x86/ioreq server: Add new functions to get/set memory types Yu Zhang
2016-04-05 13:57 ` George Dunlap
2016-04-05 14:08 ` George Dunlap
2016-04-08 13:25 ` Andrew Cooper
2016-03-31 10:53 ` [PATCH v2 2/3] x86/ioreq server: Rename p2m_mmio_write_dm to p2m_ioreq_server Yu Zhang
2016-04-05 14:38 ` George Dunlap
2016-04-08 13:26 ` Andrew Cooper
2016-04-08 21:48 ` Jan Beulich
2016-04-18 8:41 ` Paul Durrant
2016-04-18 9:10 ` George Dunlap
2016-04-18 9:14 ` Wei Liu
2016-04-18 9:45 ` Paul Durrant
2016-04-18 16:40 ` Jan Beulich
2016-04-18 16:45 ` Paul Durrant
2016-04-18 16:47 ` Jan Beulich
2016-04-18 16:58 ` Paul Durrant
2016-04-19 11:02 ` Yu, Zhang
2016-04-19 11:15 ` Paul Durrant
2016-04-19 11:38 ` Yu, Zhang
2016-04-19 11:50 ` Paul Durrant
2016-04-19 16:51 ` Jan Beulich
2016-04-20 14:59 ` Wei Liu
2016-04-20 15:02 ` George Dunlap
2016-04-20 16:30 ` George Dunlap
2016-04-20 16:52 ` Jan Beulich
2016-04-20 16:58 ` Paul Durrant
2016-04-20 17:06 ` George Dunlap
2016-04-20 17:09 ` Paul Durrant
2016-04-21 12:24 ` Yu, Zhang
2016-04-21 13:31 ` Paul Durrant
2016-04-21 13:48 ` Yu, Zhang
2016-04-21 13:56 ` Paul Durrant
2016-04-21 14:09 ` George Dunlap [this message]
2016-04-20 17:08 ` George Dunlap
2016-04-21 12:04 ` Yu, Zhang
2016-03-31 10:53 ` [PATCH v2 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server Yu Zhang
[not found] ` <20160404082556.GC28633@deinos.phlegethon.org>
2016-04-05 6:01 ` Yu, Zhang
2016-04-06 17:13 ` George Dunlap
2016-04-07 7:01 ` Yu, Zhang
[not found] ` <CAFLBxZbLp2zWzCzQTaJNWbanQSmTJ57ZyTh0qaD-+YUn8o8pyQ@mail.gmail.com>
2016-04-08 10:39 ` George Dunlap
[not found] ` <5707839F.9060803@linux.intel.com>
2016-04-08 11:01 ` George Dunlap
2016-04-11 11:15 ` Yu, Zhang
2016-04-14 10:45 ` Yu, Zhang
2016-04-18 15:57 ` Paul Durrant
2016-04-19 9:11 ` Yu, Zhang
2016-04-19 9:21 ` Paul Durrant
2016-04-19 9:44 ` Yu, Zhang
2016-04-19 10:05 ` Paul Durrant
2016-04-19 11:17 ` Yu, Zhang
2016-04-19 11:47 ` Paul Durrant
2016-04-19 11:59 ` Yu, Zhang
2016-04-20 14:50 ` George Dunlap
2016-04-20 14:57 ` Paul Durrant
2016-04-20 15:37 ` George Dunlap
2016-04-20 16:30 ` Paul Durrant
2016-04-20 16:58 ` George Dunlap
2016-04-21 13:28 ` Yu, Zhang
2016-04-21 13:21 ` Yu, Zhang
2016-04-22 11:27 ` Wei Liu
2016-04-22 11:30 ` George Dunlap
2016-04-19 4:37 ` Tian, Kevin
2016-04-19 9:21 ` Yu, Zhang
2016-04-08 13:33 ` Andrew Cooper
2016-04-11 11:14 ` Yu, Zhang
2016-04-11 12:20 ` Andrew Cooper
2016-04-11 16:25 ` Jan Beulich
2016-04-08 22:28 ` Jan Beulich
2016-04-11 11:14 ` Yu, Zhang
2016-04-11 16:31 ` Jan Beulich
2016-04-12 9:37 ` Yu, Zhang
2016-04-12 15:08 ` Jan Beulich
2016-04-14 9:56 ` Yu, Zhang
2016-04-19 4:50 ` Tian, Kevin
2016-04-19 8:46 ` Paul Durrant
2016-04-19 9:27 ` Yu, Zhang
2016-04-19 9:40 ` Paul Durrant
2016-04-19 9:49 ` Yu, Zhang
2016-04-19 10:01 ` Paul Durrant
2016-04-19 9:54 ` Yu, Zhang
2016-04-19 9:15 ` Yu, Zhang
2016-04-19 9:23 ` Paul Durrant
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