linux-kernel - Re: [PATCH v2] iommu/vt-d: avoid unnecessory panic if iommu init fail in tboot system

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Date:   Wed, 11 Nov 2020 10:17:56 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Zhenzhong Duan <zhenzhong.duan@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     baolu.lu@...ux.intel.com, ning.sun@...el.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        dwmw2@...radead.org, joro@...tes.org,
        iommu@...ts.linux-foundation.org, tboot-devel@...ts.sourceforge.net
Subject: Re: [PATCH v2] iommu/vt-d: avoid unnecessory panic if iommu init fail
 in tboot system

Hi Zhenzhong,

On 11/10/20 3:19 PM, Zhenzhong Duan wrote:
> "intel_iommu=off" command line is used to disable iommu but iommu is force
> enabled in a tboot system for security reason.
> 
> However for better performance on high speed network device, a new option
> "intel_iommu=tboot_noforce" is introduced to disable the force on.
> 
> By default kernel should panic if iommu init fail in tboot for security
> reason, but it's unnecessory if we use "intel_iommu=tboot_noforce,off".
> 
> Fix the code setting force_on and move intel_iommu_tboot_noforce
> from tboot code to intel iommu code.
> 
> Fixes: 7304e8f28bb2 ("iommu/vt-d: Correctly disable Intel IOMMU force on")
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...il.com>

Thanks for the patch.

Acked-by: Lu Baolu <baolu.lu@...ux.intel.com>

Best regards,
baolu

> ---
> v2: move ckeck of intel_iommu_tboot_noforce into iommu code per Baolu.
> 
>   arch/x86/kernel/tboot.c     | 3 ---
>   drivers/iommu/intel/iommu.c | 5 +++--
>   include/linux/intel-iommu.h | 1 -
>   3 files changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
> index 992fb14..420be87 100644
> --- a/arch/x86/kernel/tboot.c
> +++ b/arch/x86/kernel/tboot.c
> @@ -514,9 +514,6 @@ int tboot_force_iommu(void)
>   	if (!tboot_enabled())
>   		return 0;
>   
> -	if (intel_iommu_tboot_noforce)
> -		return 1;
> -
>   	if (no_iommu || swiotlb || dmar_disabled)
>   		pr_warn("Forcing Intel-IOMMU to enabled\n");
>   
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 1b1ca63..4d9b298 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -179,7 +179,7 @@ static inline unsigned long virt_to_dma_pfn(void *p)
>    * (used when kernel is launched w/ TXT)
>    */
>   static int force_on = 0;
> -int intel_iommu_tboot_noforce;
> +static int intel_iommu_tboot_noforce;
>   static int no_platform_optin;
>   
>   #define ROOT_ENTRY_NR (VTD_PAGE_SIZE/sizeof(struct root_entry))
> @@ -4885,7 +4885,8 @@ int __init intel_iommu_init(void)
>   	 * Intel IOMMU is required for a TXT/tboot launch or platform
>   	 * opt in, so enforce that.
>   	 */
> -	force_on = tboot_force_iommu() || platform_optin_force_iommu();
> +	force_on = (!intel_iommu_tboot_noforce && tboot_force_iommu()) ||
> +		    platform_optin_force_iommu();
>   
>   	if (iommu_init_mempool()) {
>   		if (force_on)
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index fbf5b3e..d956987 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -798,7 +798,6 @@ struct context_entry *iommu_context_addr(struct intel_iommu *iommu, u8 bus,
>   extern int iommu_calculate_max_sagaw(struct intel_iommu *iommu);
>   extern int dmar_disabled;
>   extern int intel_iommu_enabled;
> -extern int intel_iommu_tboot_noforce;
>   extern int intel_iommu_gfx_mapped;
>   #else
>   static inline int iommu_calculate_agaw(struct intel_iommu *iommu)
>