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Re: [Qemu-devel] [PATCH 3/7] target-arm: mark up cpregs for no-migrate o

From: Peter Maydell
Subject: Re: [Qemu-devel] [PATCH 3/7] target-arm: mark up cpregs for no-migrate or raw access
Date: Thu, 30 May 2013 23:42:37 +0100

On 30 May 2013 23:38, Christoffer Dall <address@hidden> wrote:
> On Thu, May 30, 2013 at 11:27:01PM +0100, Peter Maydell wrote:
>> On 30 May 2013 23:13, Christoffer Dall <address@hidden> wrote:
>> > CONTEXTIDR seems to be such an example. ?
>> In this specific case I decided it was safe to let the non-raw
>> write function do a tlb_flush(). Looking again that is kinda
>> expensive though, so we should probably mark these registers
>> up with raw_write functions.
> Migration is sort of an expensive operation, so not sure if it's worth
> it.

It'll also happen every time we drop out to a gdb attached
to the VM. But yes, this definitely isn't on any fast paths.

> I am mostly worries about the case where we would miss raw read/write
> functions and that could be hard to track down in the case where
> migration fails, but I don't really have great suggestions on how to
> ensure this.

That's the one argument for insisting on a raw function -- it
does mean that when looking at code and patches you can see
it's an explicit decision on how to handle the situation.

-- PMM

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