linux-kernel - Re: [PATCH] mmu notifiers #v2

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Message-ID: <Pine.LNX.4.64.0801141154240.8300@schroedinger.engr.sgi.com>
Date:	Mon, 14 Jan 2008 12:02:42 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kvm-devel@...ts.sourceforge.net, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>, daniel.blueman@...drics.com,
	holt@....com, steiner@....com, Andrew Morton <akpm@...l.org>,
	Hugh Dickins <hugh@...itas.com>, Nick Piggin <npiggin@...e.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] mmu notifiers #v2

On Sun, 13 Jan 2008, Andrea Arcangeli wrote:

> About the locking perhaps I'm underestimating it, but by following the
> TLB flushing analogy, by simply clearing the shadow ptes (with kvm
> mmu_lock spinlock to avoid racing with other vcpu spte accesses of
> course) and flushing the shadow-pte after clearing the main linux pte,
> it should be enough to serialize against shadow-pte page faults that
> would call into get_user_pages. Flushing the host TLB before or after
> the shadow-ptes shouldn't matter.

Hmmm... In most of the callsites we hold a writelock on mmap_sem right?

> Comments welcome... especially from SGI/IBM/Quadrics and all other
> potential users of this functionality.

> There are also certain details I'm uncertain about, like passing 'mm'
> to the lowlevel methods, my KVM usage of the invalidate_page()
> notifier for example only uses 'mm' for a BUG_ON for example:

Passing mm is fine as long as mmap_sem is held.

> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -86,6 +86,7 @@ do {									\
>  	pte_t __pte;							\
>  	__pte = ptep_get_and_clear((__vma)->vm_mm, __address, __ptep);	\
>  	flush_tlb_page(__vma, __address);				\
> +	mmu_notifier(invalidate_page, (__vma)->vm_mm, __address);	\
>  	__pte;								\
>  })
>  #endif

Hmmm... this is ptep_clear_flush? What about the other uses of 
flush_tlb_page in asm-generic/pgtable.h and related uses in arch code?
(would help if your patches would mention the function name in the diff 
headers)

> +#define mmu_notifier(function, mm, args...)				\
> +	do {								\
> +		struct mmu_notifier *__mn;				\
> +		struct hlist_node *__n;					\
> +									\
> +		hlist_for_each_entry(__mn, __n, &(mm)->mmu_notifier, hlist) \
> +			if (__mn->ops->function)			\
> +				__mn->ops->function(__mn, mm, args);	\
> +	} while (0)

Does this have to be inline? ptep_clear_flush will become quite big
--
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