linux-kernel - Re: [RFC PATCH v6 01/20] iommu/arm-smmu: change IOMMU_EXEC to IOMMU

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Date:	Mon, 16 Jun 2014 16:04:03 +0100
From:	Will Deacon <will.deacon@....com>
To:	Antonios Motakis <a.motakis@...tualopensystems.com>
Cc:	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"tech@...tualopensystems.com" <tech@...tualopensystems.com>,
	"a.rigo@...tualopensystems.com" <a.rigo@...tualopensystems.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"kim.phillips@...escale.com" <kim.phillips@...escale.com>,
	"stuart.yoder@...escale.com" <stuart.yoder@...escale.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	Joerg Roedel <joro@...tes.org>,
	Varun Sethi <Varun.Sethi@...escale.com>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Shuah Khan <shuah.kh@...sung.com>,
	"Upinder Malhi (umalhi)" <umalhi@...co.com>,
	"moderated list:ARM SMMU DRIVER" 
	<linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v6 01/20] iommu/arm-smmu: change IOMMU_EXEC to
 IOMMU_NOEXEC

On Thu, Jun 05, 2014 at 06:03:09PM +0100, Antonios Motakis wrote:
> Exposing the XN flag of the SMMU driver as IOMMU_NOEXEC instead of
> IOMMU_EXEC makes it enforceable, since for IOMMUs that don't support
> the XN flag pages will always be executable.
> 
> Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
> ---
>  drivers/iommu/arm-smmu.c | 2 +-
>  include/linux/iommu.h    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 647c3c7..d5a2200 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1294,7 +1294,7 @@ static int arm_smmu_alloc_init_pte(struct arm_smmu_device *smmu, pmd_t *pmd,
>  	}
>  
>  	/* If no access, create a faulting entry to avoid TLB fills */
> -	if (prot & IOMMU_EXEC)
> +	if (!(prot & IOMMU_NOEXEC))
>  		pteval &= ~ARM_SMMU_PTE_XN;

It's probably simpler to change the logic so that we initialise pteval
without XN set, then set it if IOMMU_NOEXEC is set (rather than set it
by default, then clear it if NOEXEC is not set).

Will
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