linux-kernel - Re: [PATCH 1/3] Implement emulator_write

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Message-ID: <46D2F1B7.70604@qumranet.com>
Date:	Mon, 27 Aug 2007 18:45:59 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Anthony Liguori <aliguori@...ibm.com>
CC:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Implement emulator_write_phys()

Anthony Liguori wrote:
> Since a hypercall may span two pages and is a gva, we need a function to write
> to a gva that may span multiple pages.  emulator_write_phys() seems like the
> logical choice for this.
>
> @@ -962,8 +962,35 @@ static int emulator_write_std(unsigned long addr,
>  			      unsigned int bytes,
>  			      struct kvm_vcpu *vcpu

I think that emulator_write_emulated(), except for being awkwardly 
named, should do the job.  We have enough APIs.

But!  We may not overwrite the hypercall instruction while a vcpu may be 
executing, since there's no atomicity guarantee for code fetch.  We have 
to to be out of guest mode while writing that insn.



-- 
Any sufficiently difficult bug is indistinguishable from a feature.

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