Re: [Xen-devel] [PATCH] Don't track all memory when enabling log dirty to track vram

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.02.14 at 02:28, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
> George Dunlap wrote on 2014-02-18:
>> On 02/18/2014 03:14 AM, Zhang, Yang Z wrote:
>> perhaps my original patch is better which will check
>> paging_mode_log_dirty(d) && log_global:
>> 
>> It turns out that the reason I couldn't get a crash was because libxc
>> was actually paying attention to the -EINVAL return value, and
>> disabling and then re-enabling logdirty.  That's what would happen
>> before your dirty vram patch, and that's what happens after.  And
>> arguably, that's the correct behavior for any toolstack, given that the 
> interface returns an error.
> 
> Agree.
> 
>> 
>> This patch would actually change the interface; if we check this in,
>> then if you enable logdirty when dirty vram tracking is enabled, you
>> *won't* get an error, and thus *won't* disable and re-enable logdirty mode.
>> So actually, this patch would be more disruptive.
>> 
> 
> Jan, do you have any comment? 

This simplistic variant is just calling for problems. As was already
said elsewhere on this thread, we should simply do the mode change
properly: Track that a partial log-dirty mode is in use, and allow
switching to global log-dirty mode (converting all entries to R/O).

Jan


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