linux-kernel - Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd

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Date:	Mon, 15 Jun 2015 10:05:09 +0100
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Ingo Molnar <mingo@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	xen-devel@...ts.xenproject.org,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from
 the Xen guest code

On Sat, 2015-06-13 at 11:49 +0200, Ingo Molnar wrote:
> xen_mm_pin_all()/unpin_all() are used to implement full guest instance
> suspend/restore. It's a stop-all method that needs to iterate through
> all allocated pgds in the system to fix them up for Xen's use.
> 
> This code uses pgd_list, probably because it was an easy interface.
> 
> But we want to remove the pgd_list, so convert the code over to walk
> all tasks in the system. This is an equivalent method.
> 
> (As I don't use Xen this is was only build tested.)

In which case it seems extra important to copy the appropriate
maintainers, which I've done here.

Ian.

> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Waiman Long <Waiman.Long@...com>
> Cc: linux-mm@...ck.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  arch/x86/xen/mmu.c | 51 ++++++++++++++++++++++++++++++++++++++-------------
>  1 file changed, 38 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index dd151b2045b0..70a3df5b0b54 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -853,15 +853,27 @@ static void xen_pgd_pin(struct mm_struct *mm)
>   */
>  void xen_mm_pin_all(void)
>  {
> -	struct page *page;
> +	struct task_struct *g, *p;
>  
> -	spin_lock(&pgd_lock);
> +	spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
>  
> -	list_for_each_entry(page, &pgd_list, lru) {
> -		if (!PagePinned(page)) {
> -			__xen_pgd_pin(&init_mm, (pgd_t *)page_address(page));
> -			SetPageSavePinned(page);
> +	for_each_process_thread(g, p) {
> +		struct mm_struct *mm;
> +		struct page *page;
> +		pgd_t *pgd;
> +
> +		task_lock(p);
> +		mm = p->mm;
> +		if (mm) {
> +			pgd = mm->pgd;
> +			page = virt_to_page(pgd);
> +
> +			if (!PagePinned(page)) {
> +				__xen_pgd_pin(&init_mm, pgd);
> +				SetPageSavePinned(page);
> +			}
>  		}
> +		task_unlock(p);
>  	}
>  
>  	spin_unlock(&pgd_lock);
> @@ -967,19 +979,32 @@ static void xen_pgd_unpin(struct mm_struct *mm)
>   */
>  void xen_mm_unpin_all(void)
>  {
> -	struct page *page;
> +	struct task_struct *g, *p;
>  
> -	spin_lock(&pgd_lock);
> +	spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
>  
> -	list_for_each_entry(page, &pgd_list, lru) {
> -		if (PageSavePinned(page)) {
> -			BUG_ON(!PagePinned(page));
> -			__xen_pgd_unpin(&init_mm, (pgd_t *)page_address(page));
> -			ClearPageSavePinned(page);
> +	for_each_process_thread(g, p) {
> +		struct mm_struct *mm;
> +		struct page *page;
> +		pgd_t *pgd;
> +
> +		task_lock(p);
> +		mm = p->mm;
> +		if (mm) {
> +			pgd = mm->pgd;
> +			page = virt_to_page(pgd);
> +
> +			if (PageSavePinned(page)) {
> +				BUG_ON(!PagePinned(page));
> +				__xen_pgd_unpin(&init_mm, pgd);
> +				ClearPageSavePinned(page);
> +			}
>  		}
> +		task_unlock(p);
>  	}
>  
>  	spin_unlock(&pgd_lock);
> +	rcu_read_unlock();
>  }
>  
>  static void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)


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