linux-kernel - Re: [PATCH v2] vfio/type1: Use follow

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Date:   Mon, 22 Feb 2021 11:39:11 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     alex.williamson@...hat.com
Cc:     cohuck@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, pbonzini@...hat.com, jgg@...dia.com,
        peterx@...hat.com
Subject: Re: [PATCH v2] vfio/type1: Use follow_pte()

On Tue, 16 Feb 2021 15:49:34 -0700
Alex Williamson <alex.williamson@...hat.com> 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()")
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Cornelia Huck <cohuck@...hat.com>
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
> 
> v2: Update to current follow_pte() API, add Reviews
> 
>  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..ae4fd2295c95 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, &ptep, &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, &ptep, &ptl);
> +		if (ret)
> +			return ret;
>  	}
>  
> +	if (write_fault && !pte_write(*ptep))
> +		ret = -EFAULT;
> +	else
> +		*pfn = pte_pfn(*ptep);
> +
> +	pte_unmap_unlock(ptep, ptl);
>  	return ret;
>  }
>  
> 

Adding the following to resolve 32-bit build:

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 8a777250764a..ed03f3fcb07e 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -24,6 +24,7 @@
 #include <linux/compat.h>
 #include <linux/device.h>
 #include <linux/fs.h>
+#include <linux/highmem.h>
 #include <linux/iommu.h>
 #include <linux/module.h>
 #include <linux/mm.h>