linux-kernel - Re: [PATCH 2/4] vfio/type1: batch vfio_find_vpfn() in function vfio_unpin_pages

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Message-ID: <20250703041822.37063-1-lizhe.67@bytedance.com>
Date: Thu,  3 Jul 2025 12:18:22 +0800
From: lizhe.67@...edance.com
To: jgg@...pe.ca
Cc: alex.williamson@...hat.com,
	david@...hat.com,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lizhe.67@...edance.com,
	peterx@...hat.com,
	jgg@...dia.com
Subject: Re: [PATCH 2/4] vfio/type1: batch vfio_find_vpfn() in function vfio_unpin_pages_remote()

On Wed, 2 Jul 2025 15:27:59 -0300, jgg@...pe.ca wrote:

> On Mon, Jun 30, 2025 at 03:25:16PM +0800, lizhe.67@...edance.com wrote:
> > From: Li Zhe <lizhe.67@...edance.com>
> > 
> > The function vpfn_pages() can help us determine the number of vpfn
> > nodes on the vpfn rb tree within a specified range. This allows us
> > to avoid searching for each vpfn individually in the function
> > vfio_unpin_pages_remote(). This patch batches the vfio_find_vpfn()
> > calls in function vfio_unpin_pages_remote().
> > 
> > Signed-off-by: Li Zhe <lizhe.67@...edance.com>
> > ---
> >  drivers/vfio/vfio_iommu_type1.c | 10 +++-------
> >  1 file changed, 3 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> > index a2d7abd4f2c2..330fff4fe96d 100644
> > --- a/drivers/vfio/vfio_iommu_type1.c
> > +++ b/drivers/vfio/vfio_iommu_type1.c
> > @@ -804,16 +804,12 @@ static long vfio_unpin_pages_remote(struct vfio_dma *dma, dma_addr_t iova,
> >  				    unsigned long pfn, unsigned long npage,
> >  				    bool do_accounting)
> >  {
> > -	long unlocked = 0, locked = 0;
> > +	long unlocked = 0, locked = vpfn_pages(dma, iova, npage);
> >  	long i;
> 
> The logic in vpfn_pages?() doesn't seem quite right? Don't we want  to
> count the number of pages within the range that fall within the rb
> tree?
> 
> vpfn_pages() looks like it is only counting the number of RB tree
> nodes within the range?

As I understand it, a vfio_pfn corresponds to a single page, am I right?

Thanks,
Zhe