linux-kernel - Re: [PATCH v5 08/11] thp: setup huge zero page on non-write page fault

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.00.1211151348080.27188@chino.kir.corp.google.com>
Date:	Thu, 15 Nov 2012 13:52:44 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill@...temov.name>
Subject: Re: [PATCH v5 08/11] thp: setup huge zero page on non-write page
 fault

On Thu, 15 Nov 2012, Kirill A. Shutemov wrote:

> > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > > index f36bc7d..41f05f1 100644
> > > --- a/mm/huge_memory.c
> > > +++ b/mm/huge_memory.c
> > > @@ -726,6 +726,16 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
> > >  			return VM_FAULT_OOM;
> > >  		if (unlikely(khugepaged_enter(vma)))
> > >  			return VM_FAULT_OOM;
> > > +		if (!(flags & FAULT_FLAG_WRITE)) {
> > > +			pgtable_t pgtable;
> > > +			pgtable = pte_alloc_one(mm, haddr);
> > > +			if (unlikely(!pgtable))
> > > +				goto out;
> > 
> > No use in retrying, just return VM_FAULT_OOM.
> 
> Hm. It's consistent with non-hzp path: if pte_alloc_one() in
> __do_huge_pmd_anonymous_page() fails __do_huge_pmd_anonymous_page()
> returns VM_FAULT_OOM which leads to "goto out".
> 

If the pte_alloc_one(), which wraps __pte_alloc(), you're adding fails, 
it's pointless to "goto out" to try __pte_alloc() which we know won't 
succeed.

> Should it be fixed too?
> 

It's done for maintainablility because although 
__do_huge_pmd_anonymous_page() will only return VM_FAULT_OOM today when 
pte_alloc_one() fails, if it were to ever fail in a different way then the 
caller is already has a graceful failure.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/