linux-kernel - Re: [PATCH] hugetlb: Provide a default HPAGE_SHIFT if !CONFIG_HUGETLB

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.2.00.1111162047170.13603@chino.kir.corp.google.com>
Date:	Wed, 16 Nov 2011 20:56:03 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	David Daney <ddaney.cavm@...il.com>
cc:	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] hugetlb: Provide a default HPAGE_SHIFT if
 !CONFIG_HUGETLB_PAGE

On Wed, 16 Nov 2011, David Daney wrote:

> > > It is a well established kernel idiom to supply dummy values for symbols
> > > that
> > > are required to be defined in order to form a syntactically correct C
> > > program,
> > > but that are known by the programmer to be used only on dead code paths.
> > > 
> > > This is exactly what we are doing here.
> > > 
> > > To do otherwise requires that code be cluttered with #ifdefery.
> > > 
> > 
> > You're wrong,
> 
> Ok, then please tell me why:
> 
> 1) the dummy version of is_vm_hugetlb_page() exists in hugetlb_inline.h?
> 2) the dummy version of PageHuge() exists in hugetlb.h
> 3) the dummy version of reset_vma_resv_huge_pages()
> 4) the dummy version of hugetlb_total_pages() exists in hugetlb.h
> 5) the dummy version of follow_hugetlb_page() exists in hugetlb.h
> 6) the dummy version of follow_huge_addr() exists in hugetlb.h
> 7) the dummy version of copy_hugetlb_page_range() exists in hugetlb.h
> 8) the dummy version of hugetlb_prefault() exists in hugetlb.h
> 9) the dummy version of unmap_hugepage_range() exists in hugetlb.h
> 10) the dummy version of hugetlb_report_meminfo() exists in hugetlb.h
> 11) the dummy version of hugetlb_report_node_meminfo() exists in hugetlb.h
> 12) the dummy version of follow_huge_pmd() exists in hugetlb.h
> 13) the dummy version of follow_huge_pud() exists in hugetlb.h
> 14) the dummy version of prepare_hugepage_range() exists in hugetlb.h
> 15) the dummy version of pmd_huge() exists in hugetlb.h
> 16) the dummy version of pud_huge() exists in hugetlb.h
> 17) the dummy version of is_hugepage_only_range() exists in hugetlb.h
> 17) the dummy version of hugetlb_free_pgd_range() exists in hugetlb.h
> 18) the dummy version of hugetlb_fault() exists in hugetlb.h
> 19) the dummy version of huge_pte_offset() exists in hugetlb.h
> 20) the dummy version of dequeue_hwpoisoned_huge_page() exists in hugetlb.h
> 21) the dummy version of copy_huge_page() exists in hugetlb.h
> 22) the dummy version of hugetlb_change_protection() exists in hugetlb.h
> .
> .
> .
> [Other non HUGETLB_PAGE examples omitted for conciseness]
> 

To avoid the #ifdef's, but you'll notice that they return either NULL, 0, 
or are a no-op.  We don't substitute real values in dummy functions where 
they could be used in generic code as though they were valid.  That's the 
problem with defining HPAGE_SHIFT to be PAGE_SHIFT and, yes, defining 
HPAGE_MASK and HPAGE_SIZE as well shouldn't be done and should be removed.  

We expect HPAGE_* to represent hugepages, not the native page size of the 
bare metal.  This is why we do things like

	#define HPAGE_PMD_SHIFT ({ BUG(); 0; })
	#define HPAGE_PMD_MASK ({ BUG(); 0; })
	#define HPAGE_PMD_SIZE ({ BUG(); 0; })

for CONFIG_TRANSPARENT_HUGEPAGE=n.  We don't want to pretend that they're 
valid outside the context of hugepages.

We also never use HPAGE_SHIFT, HPAGE_MASK, or HPAGE_SIZE in generic code 
that isn't dependent on CONFIG_HUGETLB_PAGE.  If you'd like to submit a 
patch to fix this in the mips tree, then that would be good, and if you'd 
like to submit a patch to remove these dummy definitions all together by 
auditing other arch code, then that would be great.
--
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/