linux-kernel - Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA

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: <CAPcyv4i8kz0UNiT05JSEp12QCMu6bKKGuMnVofSnWSg0cZF88A@mail.gmail.com>
Date:	Thu, 13 Aug 2015 11:15:40 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Matthew Wilcox <willy@...ux.intel.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>, Rik van Riel <riel@...hat.com>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	Linux MM <linux-mm@...ck.org>, Mel Gorman <mgorman@...e.de>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA

On Thu, Aug 13, 2015 at 10:35 AM, Matthew Wilcox <willy@...ux.intel.com> wrote:
> On Wed, Aug 12, 2015 at 11:01:09PM -0400, Dan Williams wrote:
>> +static inline __pfn_t page_to_pfn_t(struct page *page)
>> +{
>> +     __pfn_t pfn = { .val = page_to_pfn(page) << PAGE_SHIFT, };
>> +
>> +     return pfn;
>> +}
>
> static inline __pfn_t page_to_pfn_t(struct page *page)
> {
>         __pfn_t __pfn;
>         unsigned long pfn = page_to_pfn(page);
>         BUG_ON(pfn > (-1UL >> PFN_SHIFT))
>         __pfn.val = pfn << PFN_SHIFT;
>
>         return __pfn;
> }
>
> I have a problem wih PFN_SHIFT being equal to PAGE_SHIFT.  Consider a
> 32-bit kernel; you're asserting that no memory represented by a struct
> page can have a physical address above 4GB.
>
> You only need three bits for flags so far ... how about making PFN_SHIFT
> be 6?  That supports physical addresses up to 2^38 (256GB).  That should
> be enough, but hardware designers have done some strange things in the
> past (I know that HP made PA-RISC hardware that can run 32-bit kernels
> with memory between 64GB and 68GB, and they can't be the only strange
> hardware people out there).

Sounds good, especially given we only use 4-bits today.
--
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/