Re: [PATCH] iommu/vt-d: Fix a bug in intel_iommu_iova_to_phys() for huge page

From: Moritz Fischer <mdf@kernel.org>
To: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Yonghyun Hwang <yonghyun@google.com>,
	Havard Skinnemoen <hskinnemoen@google.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Deepa Dinamani <deepadinamani@google.com>,
	Moritz Fischer <moritzf@google.com>,
	David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH] iommu/vt-d: Fix a bug in intel_iommu_iova_to_phys() for huge page
Date: Tue, 18 Feb 2020 20:42:35 -0800	[thread overview]
Message-ID: <20200219044235.GA1397@epycbox.lan> (raw)
In-Reply-To: <8efc6ea2-d51e-624c-5cc2-4049bb224122@linux.intel.com>

Hi Baolu, Yonghyun

On Wed, Feb 19, 2020 at 11:15:36AM +0800, Lu Baolu wrote:
> Hi Yonghyun,
> 
> Thanks for the patch.
> 
> On 2020/2/19 6:23, Yonghyun Hwang wrote:
> > intel_iommu_iova_to_phys() has a bug when it translates an IOVA for a huge
> > page onto its corresponding physical address. This commit fixes the bug by
> > accomodating the level of page entry for the IOVA and adds IOVA's lower
> > address to the physical address. >
> > Signed-off-by: Yonghyun Hwang <yonghyun@google.com>
> > ---
> >   drivers/iommu/intel-iommu.c | 11 +++++++++--
> >   1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index 0c8d81f56a30..ed6e69adb578 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -5555,13 +5555,20 @@ static phys_addr_t intel_iommu_iova_to_phys(struct iommu_domain *domain,
> >   	struct dma_pte *pte;
> >   	int level = 0;
> >   	u64 phys = 0;
> > +	const unsigned long pfn = iova >> VTD_PAGE_SHIFT;
> 
> Why do you need a "const unsigned long" here?
> 
> >   	if (dmar_domain->flags & DOMAIN_FLAG_LOSE_CHILDREN)
> >   		return 0;
> > -	pte = pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT, &level);
> > -	if (pte)
> > +	pte = pfn_to_dma_pte(dmar_domain, pfn, &level);
> > +	if (pte) {
> >   		phys = dma_pte_addr(pte);
> > +		if (level > 1)
> > +			phys += (pfn &
> > +				((1UL << level_to_offset_bits(level)) - 1))
> > +				<< VTD_PAGE_SHIFT;
> > +		phys += iova & (VTD_PAGE_SIZE - 1);
> 
> How about

> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 9dc37672bf89..bd17c2510bb2 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5693,8 +5693,14 @@ static phys_addr_t intel_iommu_iova_to_phys(struct
> iommu_domain *domain,
>         u64 phys = 0;
> 
>         pte = pfn_to_dma_pte(dmar_domain, iova >> VTD_PAGE_SHIFT, &level);
> -       if (pte)
> +       if (pte) {
> +               unsigned long offset_mask;
> +
> +               offset_mask = BIT_MASK(level_to_offset_bits(level) +
> +                                      VTD_PAGE_SHIFT) - 1;
>                 phys = dma_pte_addr(pte);
> +               phys += iova & (bitmask - 1);
Did you mean:

phys += iova & (offset_mask - 1);

> +       }

At that point why not define a helper:

static inline unsigned long offset_mask(int level)
{
	return BIT_MASK(level_to_offset_bits(level) + VTD_PAGE_SHIFT) - 1;
}

At which point the above would reduce to:

if (pte)
	phys = dma_pte_addr(pte) + iova & offset_mask(level) - 1;

I might've fatfingered something here, but you get the idea :)

Cheers,
Moritz
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