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: Mon, 20 Jun 2016 17:05:08 +0800 [thread overview]
Message-ID: <5767B1C4.2070905@linux.intel.com> (raw)
In-Reply-To: <5762956E02000078000F59BD@prv-mh.provo.novell.com>
On 6/16/2016 6:02 PM, Jan Beulich wrote:
>>>> On 16.06.16 at 11:32, <yu.c.zhang@linux.intel.com> wrote:
>>> On 6/14/2016 6:45 PM, Jan Beulich wrote:
>>>>>>>> On 19.05.16 at 11:05, <yu.c.zhang@linux.intel.com> wrote:
>>>>>> @@ -914,6 +916,45 @@ int hvm_unmap_io_range_from_ioreq_server(struct domain
>>>> *d, ioservid_t id,
>>>>>> return rc;
>>>>>> }
>>>>>>
>>>>>> +int hvm_map_mem_type_to_ioreq_server(struct domain *d, ioservid_t id,
>>>>>> + uint16_t type, uint32_t flags)
>>>>> I see no reason why both can't be unsigned int.
>>>> Parameter type is passed in from the type field inside struct
>>>> xen_hvm_map_mem_type_to_ioreq_server,
>>>> which is a uint16_t, followed with a uint16_t pad. Now I am wondering,
>>>> may be we can just remove the pad
>>>> field in this structure and just define type as uint32_t.
>>> I think keeping the interface structure unchanged is the desirable
>>> route here. What I dislike is the passing around of non-natural
>>> width types, which is more expensive in terms of processing. I.e.
>>> as long as a fixed width type (which is necessary to be used in
>>> the public interface) fits in "unsigned int", that should be the
>>> respective internal type. Otherwise "unsigned long" etc.
>>>
>>> There are cases where even internally we indeed want to use
>>> fixed width types, and admittedly there are likely far more cases
>>> where internally fixed width types get used without good reason,
>>> but just like everywhere else - let's please not make this worse.
>>> IOW please use fixed width types only when you really need them.
>> OK. I can keep the interface, and using uint32_t type in the internal
>> routine
>> would means a implicit type conversion from uint16_6, which I do not think
>> is a problem.
> Just to reiterate: Unless there is a specific need, please avoid
> fixed width integer types for any internal use.
>
>>>>>> @@ -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.
>
Hi Andrew, sorry to bother you. Any comments on this? Thanks! :)
Yu
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next prev parent reply other threads:[~2016-06-20 9:05 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
2016-06-16 12:43 ` Jan Beulich
2016-06-20 9:05 ` Yu Zhang [this message]
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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