linux-kernel - Re: [PATCH 8/8] KVM: PPC: Add hugepage support for IOMMU in-kernel handling

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Message-Id: <B526C260-1ADB-4B9F-B80A-46E5A9E53FF6@suse.de>
Date:	Thu, 11 Jul 2013 14:50:04 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alexey Kardashevskiy <aik@...abs.ru>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 8/8] KVM: PPC: Add hugepage support for IOMMU in-kernel handling


On 11.07.2013, at 14:37, Benjamin Herrenschmidt wrote:

> On Thu, 2013-07-11 at 11:52 +0200, Alexander Graf wrote:
>>> Where exactly (it is rather SPAPR_TCE_IOMMU but does not really
>> matter)?
>>> Select it on KVM_BOOK3S_64? CONFIG_KVM_BOOK3S_64_HV?
>>> CONFIG_KVM_BOOK3S_64_PR? PPC_BOOK3S_64?
>> 
>> I'd say the most logical choice would be to check the Makefile and see
>> when it gets compiled. For those cases we want it enabled.
> 
> What *what* gets compiled ? You know our Makefile, it's crap :-)
> 
> We enable built-in things when CONFIG_KVM=m (which means you cannot take
> a kernel build with CONFIG_KVM not set, enable CONFIG_KVM=m, and just
> build the module, it won't work).
> 
> We could use KVM_BOOK3S_64 maybe ?

If either a =m or a =y option selects a =y option, it gets selected regardless, no? So it shouldn't really matter where we attach it FWIW.

> 
>>> I am trying to imagine a configuration where we really do not want
>>> IOMMU_API. Ben mentioned PPC32 and embedded PPC64 and that's it so
>> any of
>>> BOOK3S (KVM_BOOK3S_64 is the best) should be fine, no?
>> 
>> book3s_32 doesn't want this, but any book3s_64 implementation could
>> potentially use it, yes. That's pretty much what the Makefile tells
>> you too :).
> 
> Not really no. But that would do. You could have give a more useful
> answer in the first place though rather than stringing him along.

Sorry, I figured it was obvious.


Alex

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