linux-kernel - Re: Question about domain

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Message-ID: <bd1fd204-3596-b16c-5617-7e691ceac83b@linux.intel.com>
Date:   Thu, 26 Nov 2020 19:01:36 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jerry Snitselaar <jsnitsel@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        stable@...nel.vger.org
Cc:     baolu.lu@...ux.intel.com
Subject: Re: Question about domain_init (v5.3-v5.7)

Hi Jerry,

On 2020/11/26 4:27, Jerry Snitselaar wrote:
> 
> Is there a reason we check the requested guest address width against the
> iommu's mgaw, instead of the agaw that we already know for the iommu?
> I've run into a case with a new system where the mgaw reported is 57,
> but if they set PAE to 46 instead of 52 in the bios, then sagaw reports
> the highest supported agaw is 48 and the domain_init code fails here. In

Isn't this a platform bug? If it's too late to fix it in the BIOS, you
maybe have to add a platform specific quirk to set mgaw to the highest
supported agaw?

Best regards,
baolu

> other places like prepare_domain_attach_device, the dmar domain agaw
> gets adjusted down to the iommu agaw. The agaw of the iommu gets
> determined based off what is reported for sagaw. I'm wondering if it
> can't instead do:
> 
> ---
>   drivers/iommu/intel-iommu.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 6ca5c92ef2e5..a8e41ec36d9e 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -1862,8 +1862,8 @@ static int domain_init(struct dmar_domain *domain, struct intel_iommu *iommu,
>   	domain_reserve_special_ranges(domain);
> 
>   	/* calculate AGAW */
> -	if (guest_width > cap_mgaw(iommu->cap))
> -	        guest_width = cap_mgaw(iommu->cap);
> +	if (guest_width > agaw_to_width(iommu->agaw))
> +	        guest_width = agaw_to_width(iommu->agaw);
>   	domain->gaw = guest_width;
>   	adjust_width = guestwidth_to_adjustwidth(guest_width);
>   	agaw = width_to_agaw(adjust_width);
> --
> 2.27.0
> 
> 
> Thoughts? With the former code the ehci device for the ilo fails when
> trying to get a private domain.
> 
> Thanks,
> Jerry
>