linux-kernel - RE: [Xen-devel] [PATCH v4] modify the IO_TLB_SEGSIZE and IO_TLB_DEFAULT_SIZE configurable as flexible requirement about SW-IOMMU.

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Message-Id: <54E46ACA0200007800060F5C@mail.emea.novell.com>
Date:	Wed, 18 Feb 2015 09:34:50 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Xiaoming Wang" <xiaoming.wang@...el.com>
Cc:	"chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>,
	"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"linux@...izon.com" <linux@...izon.com>,
	"Chuansheng Liu" <chuansheng.liu@...el.com>,
	"Dongxing Zhang" <dongxing.zhang@...el.com>,
	"takahiro.akashi@...aro.org" <takahiro.akashi@...aro.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"d.kasatkin@...sung.com" <d.kasatkin@...sung.com>,
	"pebolle@...cali.nl" <pebolle@...cali.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Xen-devel] [PATCH v4] modify the IO_TLB_SEGSIZE and
 IO_TLB_DEFAULT_SIZE configurable as flexible requirement about
 SW-IOMMU.

>>> On 18.02.15 at 10:09, <xiaoming.wang@...el.com> wrote:
>> From: Jan Beulich [mailto:JBeulich@...e.com]
>> Sent: Tuesday, February 17, 2015 6:09 PM
>> >>> On 17.02.15 at 07:51, <xiaoming.wang@...el.com> wrote:
>> > --- a/Documentation/kernel-parameters.txt
>> > +++ b/Documentation/kernel-parameters.txt
>> > @@ -3438,10 +3438,12 @@ bytes respectively. Such letter suffixes can
>> > also be entirely omitted.
>> >  			it if 0 is given (See
>> Documentation/cgroups/memory.txt)
>> >
>> >  	swiotlb=	[ARM,IA-64,PPC,MIPS,X86]
>> > -			Format: { <int> | force }
>> > +			Format: { <int> | force | <int> | <int>}
>> >  			<int> -- Number of I/O TLB slabs
>> >  			force -- force using of bounce buffers even if they
>> >  			         wouldn't be automatically used by the kernel
>> > +			<int> -- Maximum allowable number of contiguous
>> slabs to map
>> > +			<int> -- The size of SW-MMU mapped.
>> 
>> This makes no sense - the new numbers added aren't position independent
>> (nor were the previous <int> and "force").
>> 
> Use ","  can separate them one by one.
> We do it at lib/swiotlb.c

Right, but the documentation above doesn't say so.

>> Also you are (supposedly) removing all uses of IO_TLB_DEFAULT_SIZE, yet
>> you don't seem to remove the definition itself.
>> 
> I have change all uses of IO_TLB_DEFAULT_SIZE to io_tlb_default_size in 
> lib/swiotlb.c

Then are there any left elsewhere? If not, again - why don't you
remove the definition of IO_TLB_DEFAULT_SIZE?

>> Finally - are arbitrary numbers really okay for the newly added command line
>> options? I.e. shouldn't you add some checking of their validity?
>> 
> I have validity these code is OK.
> Example:
> BOARD_KERNEL_CMDLINE += swiotlb=, ,512,268435456
> Io_tlb_segsize has been changed from 128 to 512
> Io_tlb_default_size has been changed from 64M to 268435456  (256M)

I specifically said "arbitrary numbers", which in particular includes
zero and non-power-of-2 values. If there are any restrictions on
which numbers can validly be passed here (and it very much looks
like there are), such restrictions should be enforced imo.

Jan

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