From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Yu, Zhang" Subject: Re: [PATCH v2 1/2] Resize the MAX_NR_IO_RANGES for ioreq server Date: Wed, 08 Jul 2015 00:02:25 +0800 Message-ID: <559BF811.8010505@linux.intel.com> References: <1436163912-1506-1-git-send-email-yu.c.zhang@linux.intel.com> <9AAE0902D5BC7E449B7C8E4E778ABCD02598AEEF@AMSPEX01CL02.citrite.net> <9AAE0902D5BC7E449B7C8E4E778ABCD02598B096@AMSPEX01CL02.citrite.net> <559A826E.1000905@eu.citrix.com> <9AAE0902D5BC7E449B7C8E4E778ABCD02598B222@AMSPEX01CL02.citrite.net> <559B8AD2.4090806@linux.intel.com> <9AAE0902D5BC7E449B7C8E4E778ABCD02598C7B8@AMSPEX01CL02.citrite.net> <559BE7D2020000780008D715@mail.emea.novell.com> <9AAE0902D5BC7E449B7C8E4E778ABCD02598D2B4@AMSPEX01CL02.citrite.net> <559BF881020000780008D83D@mail.emea.novell.com> <559BE283.80001 07@linux.intel.com> <559C01C2020000780008D8EC@mail.emea.novell.com> <559BE6F6.4020403@linux.intel.com> <559C0820020000780008D965@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <559C0820020000780008D965@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: Kevin Tian , "Keir (Xen.org)" , Andrew Cooper , George Dunlap , "xen-devel@lists.xen.org" , Paul Durrant , "zhiyuan.lv@intel.com" List-Id: xen-devel@lists.xenproject.org On 7/7/2015 11:10 PM, Jan Beulich wrote: >>>> On 07.07.15 at 16:49, wrote: >> On 7/7/2015 10:43 PM, Jan Beulich wrote: >>>>>> On 07.07.15 at 16:30, wrote: >>>> I know that George and you have concerns about the differences >>>> between MMIO and guest page tables, but I do not quite understand >>>> why. :) >>> >>> But you read George's very nice description of the differences? I >>> ask because if you did, I don't see why you re-raise the question >>> above. >>> >> >> Well, yes. I guess you mean this statement: >> "the former is one or two actual ranges of a significant size; the >> latter are (apparently) thousands of ranges of one page each."? >> But I do not understand why this is abusing the io range interface. >> Does the number matters so much? :) > > Yes, we specifically set it that low so misbehaving tool stacks > (perhaps de-privileged) can't cause the hypervisor to allocate > undue amounts of memory for tracking these ranges. This > concern, btw, applies as much to the rb-rangesets. > Thanks for your explanation, Jan. : ) In fact, I have considered to add another patch to set this limit as toolstack tunable. One problem I encountered is that how to guarantee the validity of the configured value - shall not over-consume the xen heap. But I do agree there definitely should be more amendment patches. B.R. Yu > Plus the number you bump MAX_NR_IO_RANGES to is - as I > understood it - obtained phenomenologically, i.e. there's no > reason not to assume that some bigger graphics card may > need this to be further bumped. The current count is arbitrary > too, but limiting guests only in so far as there can't be more > than so many (possibly huge) MMIO ranges on the complete set > of devices passed through to it. > > And finally, the I/O ranges are called I/O ranges because they > are intended to cover I/O memory. RAM clearly isn't I/O memory, > even if it may be accessed directly by devices. > > Jan > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel > >