linux-kernel - Re: [PATCH] vfio/type1: Use follow

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Date:   Fri, 12 Feb 2021 12:30:11 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Daniel Vetter <daniel.vetter@...el.com>, <cohuck@...hat.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <pbonzini@...hat.com>, <peterx@...hat.com>
Subject: Re: [PATCH] vfio/type1: Use follow_pte()

On Fri, 12 Feb 2021 15:08:51 -0400
Jason Gunthorpe <jgg@...dia.com> wrote:

> On Fri, Feb 12, 2021 at 12:01:50PM -0700, Alex Williamson wrote:
> > follow_pfn() doesn't make sure that we're using the correct page
> > protections, get the pte with follow_pte() so that we can test
> > protections and get the pfn from the pte.
> > 
> > Fixes: 5cbf3264bc71 ("vfio/type1: Fix VA->PA translation for PFNMAP VMAs in vaddr_get_pfn()")
> > Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c |   14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index ec9fd95a138b..90715413c3d9 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -463,9 +463,11 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
> >  			    unsigned long vaddr, unsigned long *pfn,
> >  			    bool write_fault)
> >  {
> > +	pte_t *ptep;
> > +	spinlock_t *ptl;
> >  	int ret;
> >  
> > -	ret = follow_pfn(vma, vaddr, pfn);
> > +	ret = follow_pte(vma->vm_mm, vaddr, NULL, &ptep, NULL, &ptl);
> >  	if (ret) {
> >  		bool unlocked = false;
> >  
> > @@ -479,9 +481,17 @@ static int follow_fault_pfn(struct vm_area_struct *vma, struct mm_struct *mm,
> >  		if (ret)
> >  			return ret;
> >  
> > -		ret = follow_pfn(vma, vaddr, pfn);
> > +		ret = follow_pte(vma->vm_mm, vaddr, NULL, &ptep, NULL, &ptl);  
> 
> commit 9fd6dad1261a541b3f5fa7dc5b152222306e6702 in linux-next is what
> export's follow_pte and it uses a different signature:
> 
> +int follow_pte(struct mm_struct *mm, unsigned long address,
> +              pte_t **ptepp, spinlock_t **ptlp)

Thanks, I stole it off the mailing list and hadn't noticed the change.

> Recommend you send this patch for rc1 once the right stuff lands in
> Linus's tree
> 
> Otherwise it looks OK
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Thanks!

Alex