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

[Jacob Pan]

Hi Kevin,

On Fri, 19 Feb 2021 06:19:04 +0000, "Tian, Kevin" <kevin.tian@xxxxxxxxx>
wrote:

> > 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.
> 
If the host CPU does not support WP, can guest VCPU still support WP? If
so, I agree.

> 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  
> 


Thanks,

Jacob