|Subject:||Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers|
|Date:||Thu, 31 Mar 2011 16:48:29 -0500|
|User-agent:||Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:220.127.116.11) Gecko/20110223 Lightning/1.0b2 Thunderbird/3.1.8|
On 03/31/2011 04:37 PM, Michael S. Tsirkin wrote:
On Thu, Mar 31, 2011 at 04:32:44PM -0500, Anthony Liguori wrote:On 03/31/2011 04:26 PM, Michael S. Tsirkin wrote:On Thu, Mar 31, 2011 at 02:29:50PM -0500, Anthony Liguori wrote:On 03/31/2011 02:18 PM, Peter Maydell wrote:On 31 March 2011 20:01, Anthony Liguori<address@hidden> wrote:VGA is just another device. It happens to be that we treat VGA device memory as something that behaves like ram occassionally but that does not make it RAM.So, to ask a dumb question, what does make something RAM?It's a made up concept that we use to make device performance faster. Basically, RAM should include all of the memory that a reasonable device (that we control) would DMA to and has a relatively stable mapping.My take on RAM is that RAM is just another device; the only difference is that you want to be able to implement fast paths that go straight(ish) to target memory; but that's an optimisation detail, not something that makes RAM conceptually different from other devices...Right, the trouble is, if you want to treat RAM like any other device, you can't get stable mappings to it which is bad for something like vhost-net. Regards, Anthony LiguoriNot only that I guess. Removing the VGA memory with the baloon will likely also be a bad idea.It's just the equivalent of a memset(0). It would be a silly thing for a guest to do but not somethign to be concerned about. Regards, Anthony LiguoriBTW, what is IO_MEM_NOTDIRTY?
TCG needs to keep track of dirty memory in order to be able to deal with self modifying code. IO_MEM_NOTDIRTY is the state that RAM takes before the first write. I don't think IO_MEM_NOTDIRTY would ever show up in the l1_phys_map but it will show up in the iotlb. The iotlb uses the same dispatch code as the l1_phys_map though.
Regards, Anthony Liguori
I thought another way would be to replace IO_MEM_RAM with IO_MEM_DEVICE_SHADOW_RAM in these cases but no idea what the right value for that enum would be.
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