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Re: [PATCH 2/2] kvm: clear dirty bitmaps from all overlapping memslots
From: |
Paolo Bonzini |
Subject: |
Re: [PATCH 2/2] kvm: clear dirty bitmaps from all overlapping memslots |
Date: |
Fri, 20 Sep 2019 16:03:00 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 20/09/19 14:18, Peter Xu wrote:
> (1) memory region aliasing, hence multiple GPAs can point to the same
> HVA/HPA so we need to clear the memslot dirty bits on all the
> mapped GPAs, and,
>
> (2) large log_clear() request which can cover more than one valid
> kvm memslots. Note that in this case, the mem slots can really
> be having different HVAs so imho it should be a different issue
> comparing to (1)
>
> The commit message says it's solving problem (1). However for what I
> understand, we are actually doing well on issue (1) because in
> memory_region_clear_dirty_bitmap() we iterate over all the flat views
> so that we should have caught all the aliasing memory regions if there
> are any.
There could be two addresses pointing to the same HVA *in the same
flatview*. See for example 0xe0000..0xfffff and 0xffffe000..0xffffffff
when a PC guest is started. In this particular case
0xffffe000..0xffffffff is ROM, so it's not an issue, but in other cases
it may
> However this patch should perfectly fix problem (2). Am I right?
I hadn't thought of problem (2). I guess without Igor's work for s390
it does not exist? But yes, it fixes it just the same.
Paolo