linux-kernel - Re: linux-next: manual merge of the kvm-ppc tree with the powerpc-merge tree

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Message-Id: <CDB8B53D-EEC2-41A4-9BEA-66783409EE66@suse.de>
Date:	Thu, 11 Oct 2012 17:56:51 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Scott Wood <scottwood@...escale.com>
Cc:	Tabi Timur-B04825 <B04825@...escale.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: linux-next: manual merge of the kvm-ppc tree with the powerpc-merge tree


On 11.10.2012, at 17:50, Scott Wood wrote:

> On 10/11/2012 08:04:58 AM, Alexander Graf wrote:
>> On 11.10.2012, at 05:32, Tabi Timur-B04825 wrote:
>> > On Wed, Oct 10, 2012 at 9:47 PM, Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>> >
>> >> Commit 549d62d889b4 ("KVM: PPC: use definitions in epapr header
>> >> for hcalls") from the kvm-ppc tree added an include of asm/epapr_hcall.h
>> >> to the user visible part of asm/kvm_para.h so asm/epapr_hcall.h became a
>> >> user visible header file.
>> >
>> > Any real user-space code that tries to call any of the functions in
>> > epapr_hcall.h will cause an exception.
> 
> Actually it'll cause a linker error, as of the "Don't use hardcoded opcode for ePAPR hcall invocation" patch.
> 
>> > Claiming that kernel header files that KVM needs are suddenly
>> > user-space header files doesn't make much sense to me, but I guess
>> > it's not my decision.
>> This is about kvm_host.h, which is the part that is exported to user space. It usually contains constants and structs that are required for the API.
> 
> s/kvm_host/kvm_para/
> 
> I'm not sure anything in kvm_para.h or epapr_hcalls.h would be of use to userspace, but it would be of use to the guest OS, so it's still not kernel-internal.
> 
> The variable externs should be #ifdef __KERNEL__ as David points out.  The asm stuff could still be useful in a guest OS if the guest provides epapr_hypercall_start.

I don't think we should worry about guest kernel code potentially having use for this. Let's make the user space headers be great for user space usage, not for guest code usage :).

Alex--
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