linux-kernel - Re: [PATCH 1/2] x86/amd-iommu: enable iommu before attaching devices

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Message-ID: <20100402091118.GM24846@8bytes.org>
Date:	Fri, 2 Apr 2010 11:11:18 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Joerg Roedel <joerg.roedel@....com>,
	Neil Horman <nhorman@...hat.com>,
	Neil Horman <nhorman@...driver.com>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, hbabu@...ibm.com,
	iommu@...ts.linux-foundation.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 1/2] x86/amd-iommu: enable iommu before attaching
	devices

On Thu, Apr 01, 2010 at 06:23:53PM -0700, Chris Wright wrote:
> Hit another kdump problem as reported by Neil Horman.  When initializaing
> the IOMMU, we attach devices to their domains before the IOMMU is
> fully (re)initialized.  Attaching a device will issue some important
> invalidations.  In the context of the newly kexec'd kdump kernel, the
> IOMMU may have stale cached data from the original kernel.  Because we
> do the attach too early, the invalidation commands are placed in the new
> command buffer before the IOMMU is updated w/ that buffer.  This leaves
> the stale entries in the kdump context and can renders device unusable.
> Simply enable the IOMMU before we do the attach.
> 
> Cc: Neil Horman <nhorman@...driver.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Signed-off-by: Chris Wright <chrisw@...s-sol.org>
> ---
>  arch/x86/kernel/amd_iommu_init.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/kernel/amd_iommu_init.c
> +++ b/arch/x86/kernel/amd_iommu_init.c
> @@ -1288,6 +1288,8 @@ static int __init amd_iommu_init(void)
>  	if (ret)
>  		goto free;
>  
> +	enable_iommus();
> +
>  	if (iommu_pass_through)
>  		ret = amd_iommu_init_passthrough();
>  	else
> @@ -1300,8 +1302,6 @@ static int __init amd_iommu_init(void)
>  
>  	amd_iommu_init_notifier();
>  
> -	enable_iommus();
> -
>  	if (iommu_pass_through)
>  		goto out;

Ok, good to know this fixes the problem. One issue: If the
initialization of the domains fails the iommu hardware needs to be
disabled again in the free path.

Thanks,

	Joerg

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