From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:42412) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QN6Q6-000259-FR for qemu-devel@nongnu.org; Thu, 19 May 2011 12:49:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QN6Q5-0001c4-Ck for qemu-devel@nongnu.org; Thu, 19 May 2011 12:49:54 -0400 Received: from thoth.sbs.de ([192.35.17.2]:31188) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QN6Q5-0001bg-2I for qemu-devel@nongnu.org; Thu, 19 May 2011 12:49:53 -0400 Message-ID: <4DD54A2C.6050706@siemens.com> Date: Thu, 19 May 2011 18:49:48 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <4DD51FDA.3010107@codemonkey.ws> <4DD520ED.8010606@redhat.com> <4DD5260A.1080309@codemonkey.ws> <4DD5272F.5000003@siemens.com> <4DD52848.6030102@codemonkey.ws> <4DD52910.4080106@siemens.com> <4DD52B0E.2080604@codemonkey.ws> <4DD52BF2.2080506@redhat.com> <20110519161731.GA27310@redhat.com> <4DD5446A.6030003@siemens.com> <20110519162805.GC27310@redhat.com> <4DD545B2.70705@siemens.com> <4DD54729.8050707@codemonkey.ws> In-Reply-To: <4DD54729.8050707@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC] Memory API List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Avi Kivity , Gleb Natapov , qemu-devel On 2011-05-19 18:36, Anthony Liguori wrote: > On 05/19/2011 11:30 AM, Jan Kiszka wrote: >> On 2011-05-19 18:28, Gleb Natapov wrote: >>> On Thu, May 19, 2011 at 06:25:14PM +0200, Jan Kiszka wrote: >>>> On 2011-05-19 18:17, Gleb Natapov wrote: >>>>> On Thu, May 19, 2011 at 05:40:50PM +0300, Avi Kivity wrote: >>>>>> On 05/19/2011 05:37 PM, Anthony Liguori wrote: >>>>>>> >>>>>>> So.... do you do: >>>>>>> >>>>>>> isa_register_region(ISABus *bus, MemoryRegion *mr, int priority) >>>>>>> { >>>>>>> chipset_register_region(bus->chipset, mr, priority + 1); >>>>>>> } >>>>>>> >>>>>>> I don't really understand how you can fold everything into one >>>>>>> table and not allow devices to override their parents using >>>>>>> priorities. >>>>>> >>>>>> Think of how a window manager folds windows with priorities onto a >>>>>> flat framebuffer. >>>>>> >>>>>> You do a depth-first walk of the tree. For each child list, you >>>>>> iterate it from the lowest to highest priority, allowing later >>>>>> subregions override earlier subregions. >>>>>> >>>>> And how you set those priorities in a sensible way? Why two device on a >>>>> PCI bus will want to register their memory region with anything but >>>>> highest priority? And if you let PCI subsystem to assign priorities how >>>>> it will coordinate with ISA subsystem/memory controller what priorities >>>>> to assign to get meaningful system? >>>> >>>> Priorities>default will only be used for explicit overlays, e.g. RAM >>>> over MMIO in PAM regions. Non-default priorities won't be assigned to >>>> normal PCI bars or any other device's region. >>>> >>> That does not explain who and how assign those priorities in globally >>> meaningful way. >> >> There are no global priorities. Priorities are only used inside each >> level of the memory region hierarchy to generate a resulting, flattened >> view for the next higher level. At that level, everything imported from >> below has the default prio again, ie. the lowest one. > > Then SMM is impossible. For sure it is. The CPU and the chipset, each at their mapping level, create a corresponding RAM region and register it with higher prio at the SMRAM start address (CPU and chipset will need to exchange that address or otherwise coordinate the mapping information - the price for per-CPU SMRAM). > > Why do we need priorities at all? There should be no overlap at each > level in the hierarchy. > > If you have overlapping BARs, the PCI bus will always send the request > to a single device based on something that's implementation specific. > This works because each PCI device advertises the BAR locations and > sizes in it's config space. That's not a use case for priorities at all. Priorities are useful for PAM and SMRAM-like scenarios. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux