From: Avi Kivity <avi@redhat.com>
To: Stephen Donnelly <sfdonnelly@gmail.com>
Cc: Cam Macdonell <cam@cs.ualberta.ca>,
"kvm@vger.kernel.org list" <kvm@vger.kernel.org>
Subject: Re: R/W HG memory mappings with kvm?
Date: Mon, 24 Aug 2009 07:55:24 +0300 [thread overview]
Message-ID: <4A921D3C.6020809@redhat.com> (raw)
In-Reply-To: <5f370d430908231459q4c8cfe3j62c49e33a160ab71@mail.gmail.com>
On 08/24/2009 12:59 AM, Stephen Donnelly wrote:
> On Thu, Aug 20, 2009 at 12:14 AM, Avi Kivity<avi@redhat.com> wrote:
>
>> On 08/13/2009 07:07 AM, Stephen Donnelly wrote:
>>
>>> npages = get_user_pages_fast(addr, 1, 1, page); returns -EFAULT,
>>> presumably because (vma->vm_flags& (VM_IO | VM_PFNMAP)).
>>>
>>> It takes then unlikely branch, and checks the vma, but I don't
>>> understand what it is doing here: pfn = ((addr - vma->vm_start)>>
>>> PAGE_SHIFT) + vma->vm_pgoff;
>>>
>> It's calculating the pfn according to pfnmap rules.
>>
> From what I understand this will only work when remapping 'main
> memory', e.g. where the pgoff is equal to the physical page offset?
> VMAs that remap IO memory will usually set pgoff to 0 for the start of
> the mapping.
>
If so, how do they calculate the pfn when mapping pages? kvm needs to
be able to do the same thing.
>>> In my case addr == vma->vm_start, and vma->vm_pgoff == 0, so pfn ==0.
>>>
>> How did you set up that vma? It should point to the first pfn of your
>> special memory area.
>>
> The vma was created with a remap_pfn_range call from another driver.
> Because this call sets VM_PFNMAP and VM_IO any get_user_pages(_fast)
> calls will fail.
>
> In this case the host driver was actually just remapping host memory,
> so I replaced the remap_pfn_range call with a nopage/fault vm_op. This
> allows the get_user_pages_fast call to succeed, and the mapping now
> works as expected. This is sufficient for my work at the moment.
>
>
Well if the fix is correct we need it too.
> I'm still not sure how genuine IO memory (mapped from a driver to
> userspace with remap_pfn_range or io_remap_page_range) could be mapped
> into kvm though.
>
If it can be mapped to userspace, it can be mapped to kvm. We just need
to synchronize the rules.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2009-08-24 4:54 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-05 22:41 R/W HG memory mappings with kvm? Stephen Donnelly
2009-07-06 7:38 ` Avi Kivity
2009-07-07 22:23 ` Stephen Donnelly
2009-07-08 4:36 ` Avi Kivity
2009-07-08 21:33 ` Stephen Donnelly
2009-07-09 8:10 ` Avi Kivity
2009-07-08 21:45 ` Cam Macdonell
2009-07-08 22:01 ` Stephen Donnelly
2009-07-09 6:01 ` Cam Macdonell
2009-07-09 22:38 ` Stephen Donnelly
2009-07-10 17:03 ` Cam Macdonell
2009-07-12 21:28 ` Stephen Donnelly
2009-07-14 22:25 ` [PATCH] Support shared memory device PCI device Cam Macdonell
[not found] ` <5f370d430907262256rd7f9fdalfbbec1f9492ce86@mail.gmail.com>
2009-07-27 14:48 ` R/W HG memory mappings with kvm? Cam Macdonell
2009-07-27 21:32 ` Stephen Donnelly
2009-07-28 8:54 ` Avi Kivity
2009-07-28 23:06 ` Stephen Donnelly
2009-08-13 4:07 ` Stephen Donnelly
2009-08-19 12:14 ` Avi Kivity
2009-08-23 21:59 ` Stephen Donnelly
2009-08-24 4:55 ` Avi Kivity [this message]
2009-08-26 10:22 ` Avi Kivity
2009-08-27 2:39 ` Stephen Donnelly
2009-08-27 2:34 ` Stephen Donnelly
2009-08-27 4:08 ` Avi Kivity
2009-08-30 22:33 ` Stephen Donnelly
2009-08-31 8:44 ` Avi Kivity
2009-08-31 21:13 ` Stephen Donnelly
2009-09-09 12:50 ` Avi Kivity
2009-07-29 23:52 ` Cam Macdonell
2009-07-30 9:31 ` Avi Kivity
2009-09-28 18:27 Tsuyoshi Ozawa
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