2002-10-17 19:04:18

by Eric Barton

Subject: kernel vaddr -> struct page

Hi,

I'm trying to turn a kernel virtual address into a struct page that I can
then pass to tcp_sendpage().

The kernel virtual address could be {kmalloc(),vmalloc(),kmap()}-ed memory,
and I guarantee that this memory will not be {kfree(),vfree(),kunmap()}-ed
until the socket has done with the page (i.e. all the data has been acked).

I'd have thought that vmalloc_to_page(kvaddr) should give me a page I could
use, since it is walking the page tables to find the pte for 'kvaddr', and
checking that the physical page is present.

However I find I'm sending garbage when I use this method.

Can anyone help me understand?

--

Cheers,
Eric

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2002-10-17 19:18:58

by Brian Gerst

Subject: Re: kernel vaddr -> struct page

Eric Barton wrote:
> Hi,
>
> I'm trying to turn a kernel virtual address into a struct page that I can
> then pass to tcp_sendpage().
>
> The kernel virtual address could be {kmalloc(),vmalloc(),kmap()}-ed memory,
> and I guarantee that this memory will not be {kfree(),vfree(),kunmap()}-ed
> until the socket has done with the page (i.e. all the data has been acked).
>
> I'd have thought that vmalloc_to_page(kvaddr) should give me a page I could
> use, since it is walking the page tables to find the pte for 'kvaddr', and
> checking that the physical page is present.
>
> However I find I'm sending garbage when I use this method.
>
> Can anyone help me understand?
>

virt_to_page()

--
Brian Gerst

2002-10-17 20:24:02

by David Miller

Subject: Re: kernel vaddr -> struct page

vmalloc_to_page() does not work on kmalloc/kmap'd memory.

On many system kmalloc memory is not even represented in the
page tables because the mapping goes through a direct bypass
window.

You need to know where the object came from to convert it
into a page properly. You should be allocating and passing
around pages internally anyways.

2002-10-17 20:26:12

by David Miller

Subject: Re: kernel vaddr -> struct page

From: Brian Gerst <[email protected]>
Date: Thu, 17 Oct 2002 15:24:49 -0400

virt_to_page()

Doesn't work on vmalloc() data, he said that was a possibility for his
case.