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Re: [Qemu-block] Virtio-BLK/SCSI write requests and data payload checksu

From: Peter Lieven
Subject: Re: [Qemu-block] Virtio-BLK/SCSI write requests and data payload checksums
Date: Tue, 18 Dec 2018 11:07:13 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

Am 18.12.18 um 10:34 schrieb Stefan Hajnoczi:
> On Mon, Dec 17, 2018 at 04:19:53PM +0100, Peter Lieven wrote:
>> Actually I don't know for sure that the address comes from the guest. In 
>> theory it could be that
>> the request from the guest was less than 4096 byte and Qemu just assigned a 
>> bounce buffer
>> to read the whole block and copied the relevant part to the guest. Can I see 
>> from the
>> address (0x7fa4354c0000) if it comes from Qemu or the guest?
> Something like this:
> $ awk '/rw-p/ { split($1, a, "-"); print $1, strtonum("0x" a[2]) - 
> strtonum("0x" a[1])}' /proc/$(pgrep qemu)/maps
> ...
> 7f01d3e00000-7f0213e00000 1073741824 <-- this must be my 1 GB guest RAM!
> ...
> Then you can check if the memory address falls within the guest RAM
> range.
> By the way, if you use special memory options (like share=on), then you
> may need to adjust the awk script since the mmap will look different.

I use hugetblfs, but from what I found in maps it seems to be guest memory 
(other running vm with a buffer collision at 0x7f52eb6c0000; the original one 
has gone).

7f52e7e00000-7f5467e00000 rw-p 00000000 00:32 38983264                   
/hugepages/qemu_back_mem.pc.ram.7f9SYs (deleted)



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