[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers

From: Anthony Liguori
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: 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

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.


Anthony Liguori
Not 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.


Anthony Liguori


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.


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.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]