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Message-ID: <CAJaqyWeeoahJZ86uFXwMhuy-tuQuvhUxekLpRDUNEs_OdNx+ow@mail.gmail.com>
Date: Thu, 15 Jan 2026 14:13:35 +0100
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Maxime Coquelin <mcoqueli@...hat.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, virtualization@...ts.linux.dev,
Stefano Garzarella <sgarzare@...hat.com>, Yongji Xie <xieyongji@...edance.com>,
linux-kernel@...r.kernel.org, Cindy Lu <lulu@...hat.com>,
Laurent Vivier <lvivier@...hat.com>
Subject: Re: [PATCH v12 09/13] vduse: take out allocations from vduse_dev_alloc_coherent
On Thu, Jan 15, 2026 at 12:59 PM Jason Wang <jasowang@...hat.com> wrote:
>
> On Thu, Jan 15, 2026 at 4:44 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >
> > On Thu, Jan 15, 2026 at 04:22:49PM +0800, Jason Wang wrote:
> > > On Thu, Jan 15, 2026 at 2:49 AM Eugenio Pérez <eperezma@...hat.com> wrote:
> > > >
> > > > The function vduse_dev_alloc_coherent will be called under rwlock in
> > > > next patches. Make it out of the lock to avoid increasing its fail
> > > > rate.
> > > >
> > > > Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
> > > > ---
> > > > v12:
> > > > * Avoid free_pages_exact(NULL, size) in case vduse_domain_alloc_coherent
> > > > fails (MST).
> > > >
> > > > v11: Remove duplicated call to free_pages_exact (Jason).
> > > > ---
> > > > drivers/vdpa/vdpa_user/iova_domain.c | 24 +++++++-----------------
> > > > drivers/vdpa/vdpa_user/iova_domain.h | 5 ++---
> > > > drivers/vdpa/vdpa_user/vduse_dev.c | 17 +++++++++++------
> > > > 3 files changed, 20 insertions(+), 26 deletions(-)
> > > >
> > > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
> > > > index 309cd5a039d1..0a9f668467a8 100644
> > > > --- a/drivers/vdpa/vdpa_user/iova_domain.c
> > > > +++ b/drivers/vdpa/vdpa_user/iova_domain.c
> > > > @@ -493,17 +493,15 @@ void vduse_domain_unmap_page(struct vduse_iova_domain *domain,
> > > > vduse_domain_free_iova(iovad, dma_addr, size);
> > > > }
> > > >
> > > > -void *vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
> > > > - size_t size, dma_addr_t *dma_addr,
> > > > - gfp_t flag)
> > > > +dma_addr_t vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
> > > > + size_t size, void *orig)
> > > > {
> > > > struct iova_domain *iovad = &domain->consistent_iovad;
> > > > unsigned long limit = domain->iova_limit;
> > > > dma_addr_t iova = vduse_domain_alloc_iova(iovad, size, limit);
> > > > - void *orig = alloc_pages_exact(size, flag);
> > > >
> > > > - if (!iova || !orig)
> > > > - goto err;
> > > > + if (!iova)
> > > > + return DMA_MAPPING_ERROR;
> > > >
> > > > spin_lock(&domain->iotlb_lock);
> > > > if (vduse_iotlb_add_range(domain, (u64)iova, (u64)iova + size - 1,
> > > > @@ -514,17 +512,12 @@ void *vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
> > > > }
> > > > spin_unlock(&domain->iotlb_lock);
> > > >
> > > > - *dma_addr = iova;
> > > > + return iova;
> > > >
> > > > - return orig;
> > > > err:
> > > > - *dma_addr = DMA_MAPPING_ERROR;
> > > > - if (orig)
> > > > - free_pages_exact(orig, size);
> > > > - if (iova)
> > > > - vduse_domain_free_iova(iovad, iova, size);
> > > > + vduse_domain_free_iova(iovad, iova, size);
> > > >
> > > > - return NULL;
> > > > + return DMA_MAPPING_ERROR;
> > > > }
> > > >
> > > > void vduse_domain_free_coherent(struct vduse_iova_domain *domain, size_t size,
> > > > @@ -533,7 +526,6 @@ void vduse_domain_free_coherent(struct vduse_iova_domain *domain, size_t size,
> > > > struct iova_domain *iovad = &domain->consistent_iovad;
> > > > struct vhost_iotlb_map *map;
> > > > struct vdpa_map_file *map_file;
> > > > - phys_addr_t pa;
> > > >
> > > > spin_lock(&domain->iotlb_lock);
> > > > map = vhost_iotlb_itree_first(domain->iotlb, (u64)dma_addr,
> > > > @@ -545,12 +537,10 @@ void vduse_domain_free_coherent(struct vduse_iova_domain *domain, size_t size,
> > > > map_file = (struct vdpa_map_file *)map->opaque;
> > > > fput(map_file->file);
> > > > kfree(map_file);
> > > > - pa = map->addr;
> > > > vhost_iotlb_map_free(domain->iotlb, map);
> > > > spin_unlock(&domain->iotlb_lock);
> > > >
> > > > vduse_domain_free_iova(iovad, dma_addr, size);
> > > > - free_pages_exact(phys_to_virt(pa), size);
> > > > }
> > > >
> > > > static vm_fault_t vduse_domain_mmap_fault(struct vm_fault *vmf)
> > > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h
> > > > index 081f06c52cdc..e50e55d1396f 100644
> > > > --- a/drivers/vdpa/vdpa_user/iova_domain.h
> > > > +++ b/drivers/vdpa/vdpa_user/iova_domain.h
> > > > @@ -65,9 +65,8 @@ void vduse_domain_unmap_page(struct vduse_iova_domain *domain,
> > > > dma_addr_t dma_addr, size_t size,
> > > > enum dma_data_direction dir, unsigned long attrs);
> > > >
> > > > -void *vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
> > > > - size_t size, dma_addr_t *dma_addr,
> > > > - gfp_t flag);
> > > > +dma_addr_t vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
> > > > + size_t size, void *orig);
> > > >
> > > > void vduse_domain_free_coherent(struct vduse_iova_domain *domain, size_t size,
> > > > dma_addr_t dma_addr, unsigned long attrs);
> > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > index 0e3cf5128ad0..6dba1f3224d9 100644
> > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > @@ -916,23 +916,27 @@ static void *vduse_dev_alloc_coherent(union virtio_map token, size_t size,
> > > > {
> > > > struct vduse_dev *vdev;
> > > > struct vduse_iova_domain *domain;
> > > > - unsigned long iova;
> > > > void *addr;
> > > >
> > > > *dma_addr = DMA_MAPPING_ERROR;
> > > > if (!token.group)
> > > > return NULL;
> > > >
> > > > - vdev = token.group->dev;
> > > > - domain = vdev->domain;
> > > > - addr = vduse_domain_alloc_coherent(domain, size,
> > > > - (dma_addr_t *)&iova, flag);
> > > > + addr = alloc_pages_exact(size, flag);
> > > > if (!addr)
> > > > return NULL;
> > > >
> > > > - *dma_addr = (dma_addr_t)iova;
> > > > + vdev = token.group->dev;
> > > > + domain = vdev->domain;
> > > > + *dma_addr = vduse_domain_alloc_coherent(domain, size, addr);
> > > > + if (*dma_addr == DMA_MAPPING_ERROR)
> > > > + goto err;
> > > >
> > > > return addr;
> > > > +
> > > > +err:
> > > > + free_pages_exact(addr, size);
> > > > + return NULL;
> > > > }
> > >
> > > I think the code tries to hide the iova domain specific things (e.g
> > > mappings and DMA_MAPPING_ERROR) from vduse core. Could we find a way
> > > to stick to that?
> > >
> > > Thanks
> >
> >
> > what do you suggest more spefically though?
>
> I think it would be better to move the dma/map stuffs to the iova_domain.c
>
I'm not sure, DMA_MAPPING_ERROR was returned by parameter already
before this series and virtio_ring.c uses it in other functions too. I
guess we could divert more from the HW DMA and trust in return value
in virtion_ring.c conditionals checking if vring_use_dma_api, but I
think to include it here is trying to add too much to this series to
be honest.
Would that work to do it on top in the future?
> Thanks
>
> >
> > > >
> > > > static void vduse_dev_free_coherent(union virtio_map token, size_t size,
> > > > @@ -949,6 +953,7 @@ static void vduse_dev_free_coherent(union virtio_map token, size_t size,
> > > > domain = vdev->domain;
> > > >
> > > > vduse_domain_free_coherent(domain, size, dma_addr, attrs);
> > > > + free_pages_exact(vaddr, size);
> > > > }
> > > >
> > > > static bool vduse_dev_need_sync(union virtio_map token, dma_addr_t dma_addr)
> > > > --
> > > > 2.52.0
> > > >
> >
>
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