linux-kernel - Re: 2.6.29 pat issue

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Message-ID: <49B6232B.4050503@vmware.com>
Date:	Tue, 10 Mar 2009 09:22:03 +0100
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: 2.6.29 pat issue

Pallipadi, Venkatesh wrote:
> On Fri, Mar 06, 2009 at 03:44:07PM -0800, Thomas Hellstrom wrote:
>   
>> We get the warning when we insert RAM pages using vm_insert_pfn().
>> Having normal RAM pages backing a PFN papping is a valid thing.
>>
>>     
>
> OK. Below is the updated patch that should fix this fully. Can you confirm?
>
> Thanks,
> Venki
>
>   

Yes, this patch should fix the problem. I'm still concerned about the 
overhead of going through the
RAM test for each inserted page.

Why can't a pfn_valid() test be used in vm_insert_pfn()?

Thanks,
Thomas



> From: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
> Subject: [PATCH] VM, x86 PAT: Change implementation of is_linear_pfn_mapping
>
> Use of vma->vm_pgoff to identify the pfnmaps that are fully mapped at
> mmap time is broken, as vm_pgoff can also be set when full mapping is
> not setup at mmap time.
> http://marc.info/?l=linux-kernel&m=123383810628583&w=2
>
> Change the logic to overload VM_NONLINEAR flag along with VM_PFNMAP to
> mean full mapping setup at mmap time. This distinction is needed by
> x86 PAT code.
>
> Regression reported at
> http://bugzilla.kernel.org/show_bug.cgi?id=12800
>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>  arch/x86/mm/pat.c  |    5 +++--
>  include/linux/mm.h |    8 +++++++-
>  mm/memory.c        |    6 ++++--
>  3 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 2ed3715..640339e 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -677,10 +677,11 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
>  	is_ram = pat_pagerange_is_ram(paddr, paddr + size);
>  
>  	/*
> -	 * reserve_pfn_range() doesn't support RAM pages.
> +	 * reserve_pfn_range() doesn't support RAM pages. Maintain the current
> +	 * behavior with RAM pages by returning success.
>  	 */
>  	if (is_ram != 0)
> -		return -EINVAL;
> +		return 0;
>  
>  	ret = reserve_memtype(paddr, paddr + size, want_flags, &flags);
>  	if (ret)
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 065cdf8..6c3fc3a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -127,6 +127,12 @@ extern unsigned int kobjsize(const void *objp);
>  #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_RESERVED | VM_PFNMAP)
>  
>  /*
> + * pfnmap vmas that are fully mapped at mmap time (not mapped on fault).
> + * Used by x86 PAT to identify such PFNMAP mappings and optimize their handling.
> + */
> +#define VM_PFNMAP_AT_MMAP (VM_NONLINEAR | VM_PFNMAP)
> +
> +/*
>   * mapping from the currently active vm_flags protection bits (the
>   * low four bits) to a page protection mask..
>   */
> @@ -145,7 +151,7 @@ extern pgprot_t protection_map[16];
>   */
>  static inline int is_linear_pfn_mapping(struct vm_area_struct *vma)
>  {
> -	return ((vma->vm_flags & VM_PFNMAP) && vma->vm_pgoff);
> +	return ((vma->vm_flags & VM_PFNMAP_AT_MMAP) == VM_PFNMAP_AT_MMAP);
>  }
>  
>  static inline int is_pfn_mapping(struct vm_area_struct *vma)
> diff --git a/mm/memory.c b/mm/memory.c
> index baa999e..d7df5ba 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1665,9 +1665,10 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
>  	 * behaviour that some programs depend on. We mark the "original"
>  	 * un-COW'ed pages by matching them up with "vma->vm_pgoff".
>  	 */
> -	if (addr == vma->vm_start && end == vma->vm_end)
> +	if (addr == vma->vm_start && end == vma->vm_end) {
>  		vma->vm_pgoff = pfn;
> -	else if (is_cow_mapping(vma->vm_flags))
> +		vma->vm_flags |= VM_PFNMAP_AT_MMAP;
> +	} else if (is_cow_mapping(vma->vm_flags))
>  		return -EINVAL;
>  
>  	vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
> @@ -1679,6 +1680,7 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
>  		 * needed from higher level routine calling unmap_vmas
>  		 */
>  		vma->vm_flags &= ~(VM_IO | VM_RESERVED | VM_PFNMAP);
> +		vma->vm_flags &= ~VM_PFNMAP_AT_MMAP;
>  		return -EINVAL;
>  	}
>  
>   

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