RE: [PATCH] vhost: fix get hpa fail from guest pages

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Xia, Chenbo <chenbo.xia@intel.com>
> Sent: Monday, November 15, 2021 4:04 PM
> To: Wang, YuanX <yuanx.wang@intel.com>; maxime.coquelin@redhat.com
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Ding, Xuan
> <xuan.ding@intel.com>; Ma, WenwuX <wenwux.ma@intel.com>; He, Xingguang
> <xingguang.he@intel.com>; Yang, YvonneX <yvonnex.yang@intel.com>
> Subject: RE: [PATCH] vhost: fix get hpa fail from guest pages
> 
> > -----Original Message-----
> > From: Wang, YuanX <yuanx.wang@intel.com>
> > Sent: Thursday, November 11, 2021 2:27 PM
> > To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> > Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Ding, Xuan
> > <xuan.ding@intel.com>; Ma, WenwuX <wenwux.ma@intel.com>; He, Xingguang
> > <xingguang.he@intel.com>; Yang, YvonneX <yvonnex.yang@intel.com>; Wang,
> YuanX
> > <yuanx.wang@intel.com>
> > Subject: [PATCH] vhost: fix get hpa fail from guest pages
> >
> > When processing front-end memory regions messages,
> > vhost saves the guest/host physical address mappings to guest pages
> > and merges adjacent contiguous pages if hpa is contiguous,
> > however gpa is likely not contiguous in PA mode
> > and merging will cause the gpa range to change.
> > This patch distinguishes the case of discontinuous gpa
> > and does a range lookup on gpa when doing a binary search.
> >
> > Fixes: e246896178e("vhost: get guest/host physical address mappings")
> > Fixes: 6563cf92380 ("vhost: fix async copy on multi-page buffers")
> >
> > Signed-off-by: Yuan Wang <yuanx.wang@intel.com>
> > ---
> >  lib/vhost/vhost.h      | 18 ++++++++++++++++--
> >  lib/vhost/vhost_user.c | 15 +++++++++++----
> >  2 files changed, 27 insertions(+), 6 deletions(-)
> >
> > diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
> > index 7085e0885c..b3f0c1d07c 100644
> > --- a/lib/vhost/vhost.h
> > +++ b/lib/vhost/vhost.h
> > @@ -587,6 +587,20 @@ static __rte_always_inline int guest_page_addrcmp(const
> > void *p1,
> >  	return 0;
> >  }
> >
> > +static __rte_always_inline int guest_page_rangecmp(const void *p1, const
> void
> > *p2)
> > +{
> > +	const struct guest_page *page1 = (const struct guest_page *)p1;
> > +	const struct guest_page *page2 = (const struct guest_page *)p2;
> > +
> > +	if (page1->guest_phys_addr >= page2->guest_phys_addr) {
> > +		if (page1->guest_phys_addr < page2->guest_phys_addr + page2->size)
> > +			return 0;
> > +		else
> > +			return 1;
> > +	} else
> > +		return -1;
> > +}
> > +
> >  static __rte_always_inline rte_iova_t
> >  gpa_to_first_hpa(struct virtio_net *dev, uint64_t gpa,
> >  	uint64_t gpa_size, uint64_t *hpa_size)
> > @@ -597,9 +611,9 @@ gpa_to_first_hpa(struct virtio_net *dev, uint64_t gpa,
> >
> >  	*hpa_size = gpa_size;
> >  	if (dev->nr_guest_pages >= VHOST_BINARY_SEARCH_THRESH) {
> > -		key.guest_phys_addr = gpa & ~(dev->guest_pages[0].size - 1);
> > +		key.guest_phys_addr = gpa;
> >  		page = bsearch(&key, dev->guest_pages, dev->nr_guest_pages,
> > -			       sizeof(struct guest_page), guest_page_addrcmp);
> > +			       sizeof(struct guest_page), guest_page_rangecmp);
> >  		if (page) {
> >  			if (gpa + gpa_size <=
> >  					page->guest_phys_addr + page->size) {
> > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> > index a781346c4d..7d58fde458 100644
> > --- a/lib/vhost/vhost_user.c
> > +++ b/lib/vhost/vhost_user.c
> > @@ -999,10 +999,17 @@ add_one_guest_page(struct virtio_net *dev, uint64_t
> > guest_phys_addr,
> >  	if (dev->nr_guest_pages > 0) {
> >  		last_page = &dev->guest_pages[dev->nr_guest_pages - 1];
> >  		/* merge if the two pages are continuous */
> > -		if (host_phys_addr == last_page->host_phys_addr +
> > -				      last_page->size) {
> > -			last_page->size += size;
> > -			return 0;
> > +		if (host_phys_addr == last_page->host_phys_addr + last_page->size)
> > {
> > +			if (rte_eal_iova_mode() == RTE_IOVA_VA) {
> > +				last_page->size += size;
> > +				return 0;
> > +			}
> 
> This makes me think about a question: In IOVA_VA mode, what ensures HPA and
> GPA are
> both contiguous?

When I wrote this email, I thought host_phys_addr is HPA but in VA mode, it's
Host IOVA, aka VA in DPDK's case. So in most cases GPA and VA will be both
contiguous when the contiguous pages are all in one memory region. But I think
we should not make such assumption as some vhost master may send GPA-contiguous
pages in different memory region, then the VA after mmap may not be contiguous.

Maxime, What do you think?

Thanks,
Chenbo

> 
> Maxime & Yuan, any thought?
> 
> Thanks,
> Chenbo
> 
> > +
> > +			if (rte_eal_iova_mode() == RTE_IOVA_PA &&
> > +				guest_phys_addr == last_page->guest_phys_addr +
> > last_page->size) {
> > +				last_page->size += size;
> > +				return 0;
> > +			}
> >  		}
> >  	}
> >
> > --
> > 2.25.1