RE: [PATCH 2/4] iommu/vt-d: Enable write protect propagation from guest

[Tian, Kevin]

> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Sent: Friday, February 19, 2021 5:31 AM
> 
> Write protect bit, when set, inhibits supervisor writes to the read-only
> pages. In guest supervisor shared virtual addressing (SVA), write-protect
> should be honored upon guest bind supervisor PASID request.
> 
> This patch extends the VT-d portion of the IOMMU UAPI to include WP bit.
> WPE bit of the  supervisor PASID entry will be set to match CPU CR0.WP bit.
> 
> Signed-off-by: Sanjay Kumar <sanjay.k.kumar@xxxxxxxxx>
> Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/intel/pasid.c | 5 +++++
>  include/uapi/linux/iommu.h  | 3 ++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index 0b7e0e726ade..c7a2ec930af4 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -763,6 +763,11 @@ intel_pasid_setup_bind_data(struct intel_iommu
> *iommu, struct pasid_entry *pte,
>  			return -EINVAL;
>  		}
>  		pasid_set_sre(pte);
> +		/* Enable write protect WP if guest requested */
> +		if (pasid_data->flags & IOMMU_SVA_VTD_GPASID_WPE) {
> +			if (pasid_enable_wpe(pte))
> +				return -EINVAL;

We should call pasid_set_wpe directly, as this binding is about guest
page table and suppose the guest has done whatever check required
(e.g. gcr0.wp) before setting this bit. pasid_enable_wpe has an additional 
check on host cr0.wp thus is logically incorrect here.

Thanks
Kevin

> +		}
>  	}
> 
>  	if (pasid_data->flags & IOMMU_SVA_VTD_GPASID_EAFE) {
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> index 68cb558fe8db..33f3dc7a91de 100644
> --- a/include/uapi/linux/iommu.h
> +++ b/include/uapi/linux/iommu.h
> @@ -288,7 +288,8 @@ struct iommu_gpasid_bind_data_vtd {
>  #define IOMMU_SVA_VTD_GPASID_PWT	(1 << 3) /* page-level write
> through */
>  #define IOMMU_SVA_VTD_GPASID_EMTE	(1 << 4) /* extended mem
> type enable */
>  #define IOMMU_SVA_VTD_GPASID_CD		(1 << 5) /* PASID-level
> cache disable */
> -#define IOMMU_SVA_VTD_GPASID_LAST	(1 << 6)
> +#define IOMMU_SVA_VTD_GPASID_WPE	(1 << 6) /* Write protect
> enable */
> +#define IOMMU_SVA_VTD_GPASID_LAST	(1 << 7)
>  	__u64 flags;
>  	__u32 pat;
>  	__u32 emt;
> --
> 2.25.1