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From: Yu Zhang <yu.c.zhang@linux.intel.com>
To: Jan Beulich <JBeulich@suse.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Tim Deegan <tim@xen.org>,
	xen-devel@lists.xen.org, Paul Durrant <paul.durrant@citrix.com>,
	zhiyuan.lv@intel.com, Jun Nakajima <jun.nakajima@intel.com>
Subject: Re: [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.
Date: Thu, 16 Jun 2016 19:18:39 +0800	[thread overview]
Message-ID: <57628B0F.8010209@linux.intel.com> (raw)
In-Reply-To: <5762956E02000078000F59BD@prv-mh.provo.novell.com>



On 6/16/2016 6:02 PM, Jan Beulich wrote:
>>>>>> @@ -94,8 +96,16 @@ static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t mfn,
>>>>>>         default:
>>>>>>             return flags | _PAGE_NX_BIT;
>>>>>>         case p2m_grant_map_ro:
>>>>>> -    case p2m_ioreq_server:
>>>>>>             return flags | P2M_BASE_FLAGS | _PAGE_NX_BIT;
>>>>>> +    case p2m_ioreq_server:
>>>>>> +    {
>>>>>> +        flags |= P2M_BASE_FLAGS | _PAGE_RW;
>>>>>> +
>>>>>> +        if ( p2m->ioreq.flags & P2M_IOREQ_HANDLE_WRITE_ACCESS )
>>>>>> +            return flags & ~_PAGE_RW;
>>>>>> +        else
>>>>>> +            return flags;
>>>>>> +    }
>>>>> Same here (for the missing _PAGE_NX) plus no need for braces.
>>>> I'll remove the brace. And we do not need to set the _PAGE_NX_BIT, like
>>>> the p2m_ram_ro case I guess.
>>> I hope you mean the inverse: You should set _PAGE_NX_BIT here.
>> Oh, right. I meant the reverse. Thanks for the remind. :)
>> And I have a question,  here in p2m_type_to_flags(), I saw current code
>> uses _PAGE_NX_BIT
>> to disable the executable permission,  and I wonder, why don't we choose
>> the _PAGE_NX,
>> which is defined as:
>>
>> #define _PAGE_NX       (cpu_has_nx ? _PAGE_NX_BIT : 0)
>>
>> How do we know for sure that bit 63 from pte is not a reserved one
>> without checking
>> the cpu capability(the cpu_has_nx)? Is there any other reasons, i.e. the
>> page tables might
>> be shared with IOMMU?
> Please wait for Andrew to confirm this (or correct me) - there are
> some differences between AMD and Intel, and iirc the bit gets
> ignored by AMD when NX is off.
>
>>>>>> +struct xen_hvm_map_mem_type_to_ioreq_server {
>>>>>> +    domid_t domid;      /* IN - domain to be serviced */
>>>>>> +    ioservid_t id;      /* IN - ioreq server id */
>>>>>> +    uint16_t type;      /* IN - memory type */
>>>>>> +    uint16_t pad;
>>>>> This field does not appear to get checked in the handler.
>>>> I am now wondering, how about we remove this pad field and define type
>>>> as uint32_t?
>>> As above - I think the current layout is fine. But I'm also not heavily
>>> opposed to using uint32_t here. It's not a stable interface anyway
>>> (and I already have a series mostly ready to split off all control
>>> operations from the HVMOP_* ones, into a new HVMCTL_* set,
>>> which will make all of them interface-versioned).
>> I'd like to keep this interface. BTW, you mentioned "this field does not
>> appear to
>> get checked in the handler", do you mean we need to check the pad in the
>> handler?
> Yes.
>
>> And why?
> In order to be able to later assign meaning to it without breaking
> existing users.

So the handler need to assure the pad is 0, right?

Thanks
Yu

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  reply	other threads:[~2016-06-16 11:18 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-19  9:05 [PATCH v4 0/3] x86/ioreq server: Introduce HVMMEM_ioreq_server mem type Yu Zhang
2016-05-19  9:05 ` [PATCH v4 1/3] x86/ioreq server: Rename p2m_mmio_write_dm to p2m_ioreq_server Yu Zhang
2016-06-14 10:04   ` Jan Beulich
2016-06-14 13:14     ` George Dunlap
2016-06-15 10:51     ` Yu Zhang
2016-05-19  9:05 ` [PATCH v4 2/3] x86/ioreq server: Add new functions to get/set memory types Yu Zhang
2016-05-19  9:05 ` [PATCH v4 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server Yu Zhang
2016-06-14 10:45   ` Jan Beulich
2016-06-14 13:13     ` George Dunlap
2016-06-14 13:31       ` Jan Beulich
2016-06-15  9:50         ` George Dunlap
2016-06-15 10:21           ` Jan Beulich
2016-06-15 11:28             ` George Dunlap
2016-06-16  9:30             ` Yu Zhang
2016-06-16  9:55               ` Jan Beulich
2016-06-17 10:17                 ` George Dunlap
2016-06-20  9:03                   ` Yu Zhang
2016-06-20 10:10                     ` George Dunlap
2016-06-20 10:25                       ` Jan Beulich
2016-06-20 10:32                         ` George Dunlap
2016-06-20 10:55                           ` Jan Beulich
2016-06-20 11:28                             ` Yu Zhang
2016-06-20 13:13                               ` George Dunlap
2016-06-21  7:42                                 ` Yu Zhang
2016-06-20 10:30                       ` Yu Zhang
2016-06-20 10:43                         ` George Dunlap
2016-06-20 10:45                         ` Jan Beulich
2016-06-20 11:06                           ` Yu Zhang
2016-06-20 11:20                             ` Jan Beulich
2016-06-20 12:06                               ` Yu Zhang
2016-06-20 13:38                                 ` Jan Beulich
2016-06-21  7:45                                   ` Yu Zhang
2016-06-21  8:22                                     ` Jan Beulich
2016-06-21  9:16                                       ` Yu Zhang
2016-06-21  9:47                                         ` Jan Beulich
2016-06-21 10:00                                           ` Yu Zhang
2016-06-21 14:38                                           ` George Dunlap
2016-06-22  6:39                                             ` Jan Beulich
2016-06-22  8:38                                               ` Yu Zhang
2016-06-22  9:11                                                 ` Jan Beulich
2016-06-22  9:16                                               ` George Dunlap
2016-06-22  9:29                                                 ` Jan Beulich
2016-06-22  9:47                                                   ` George Dunlap
2016-06-22 10:07                                                     ` Yu Zhang
2016-06-22 11:33                                                       ` George Dunlap
2016-06-23  7:37                                                         ` Yu Zhang
2016-06-23 10:33                                                           ` George Dunlap
2016-06-24  4:16                                                             ` Yu Zhang
2016-06-24  6:12                                                               ` Jan Beulich
2016-06-24  7:12                                                                 ` Yu Zhang
2016-06-24  8:01                                                                   ` Jan Beulich
2016-06-24  9:57                                                                     ` Yu Zhang
2016-06-24 10:27                                                                       ` Jan Beulich
2016-06-22 10:10                                                     ` Jan Beulich
2016-06-22 10:15                                                       ` George Dunlap
2016-06-22 11:50                                                         ` Jan Beulich
2016-06-15 10:52     ` Yu Zhang
2016-06-15 12:26       ` Jan Beulich
2016-06-16  9:32         ` Yu Zhang
2016-06-16 10:02           ` Jan Beulich
2016-06-16 11:18             ` Yu Zhang [this message]
2016-06-16 12:43               ` Jan Beulich
2016-06-20  9:05             ` Yu Zhang
2016-06-14 13:14   ` George Dunlap
2016-05-27  7:52 ` [PATCH v4 0/3] x86/ioreq server: Introduce HVMMEM_ioreq_server mem type Zhang, Yu C
2016-05-27 10:00   ` Jan Beulich
2016-05-27  9:51     ` Zhang, Yu C
2016-05-27 10:02     ` George Dunlap

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