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Message-ID: <20230310095220.5dc3d8ac@jacob-builder>
Date: Fri, 10 Mar 2023 09:52:20 -0800
From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
Jason Gunthorpe <jgg@...dia.com>,
Joerg Roedel <joro@...tes.org>,
Jean-Philippe Brucker <jean-philippe@...aro.com>,
Dave Hansen <dave.hansen@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
X86 Kernel <x86@...nel.org>, bp@...en8.de,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>, corbet@....net,
vkoul@...nel.org, dmaengine@...r.kernel.org,
linux-doc@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
Will Deacon <will@...nel.org>,
David Woodhouse <dwmw2@...radead.org>,
Raj Ashok <ashok.raj@...el.com>,
"Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
"Yu, Fenghua" <fenghua.yu@...el.com>,
Dave Jiang <dave.jiang@...el.com>,
Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
Tony Luck <tony.luck@...el.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v5 4/7] iommu/sva: Stop using ioasid_set for SVA
Hi Baolu,
On Fri, 10 Mar 2023 13:07:51 +0800, Baolu Lu <baolu.lu@...ux.intel.com>
wrote:
> On 3/10/23 6:21 AM, Jacob Pan wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> >
> > Instead SVA drivers can use a simple global IDA to allocate PASIDs for
> > each mm_struct.
> >
> > Future work would be to allow drivers using the SVA APIs to reserve
> > global PASIDs from this IDA for their internal use, eg with the DMA API
> > PASID support.
> >
> > Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > ---
> > v5:
> > - Put removing iommu_sva_find() to a separate patch (Kevin)
> > - Make pasid allocation range to be inclusive (Tina)
> > - Simplified return code handling (Baolu)
> > v4:
> > - Keep GFP_ATOMIC flag for PASID allocation, will changed to
> > GFP_KERNEL in a separate patch.
> > ---
> > drivers/iommu/iommu-sva.c | 42 +++++++++++++--------------------------
> > drivers/iommu/iommu-sva.h | 2 --
> > 2 files changed, 14 insertions(+), 30 deletions(-)
> >
> > diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> > index 4f357ef14f04..b75711bdbe97 100644
> > --- a/drivers/iommu/iommu-sva.c
> > +++ b/drivers/iommu/iommu-sva.c
> > @@ -9,47 +9,33 @@
> > #include "iommu-sva.h"
> >
> > static DEFINE_MUTEX(iommu_sva_lock);
> > -static DECLARE_IOASID_SET(iommu_sva_pasid);
> > +static DEFINE_IDA(iommu_global_pasid_ida);
> >
> > -/**
> > - * iommu_sva_alloc_pasid - Allocate a PASID for the mm
> > - * @mm: the mm
> > - * @min: minimum PASID value (inclusive)
> > - * @max: maximum PASID value (inclusive)
> > - *
> > - * Try to allocate a PASID for this mm, or take a reference to the
> > existing one
> > - * provided it fits within the [@min, @max] range. On success the
> > PASID is
> > - * available in mm->pasid and will be available for the lifetime of
> > the mm.
> > - *
> > - * Returns 0 on success and < 0 on error.
> > - */
> > -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t
> > max) +static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t
> > min, ioasid_t max) {
> > int ret = 0;
> > - ioasid_t pasid;
> >
> > - if (min == INVALID_IOASID || max == INVALID_IOASID ||
> > - min == 0 || max < min)
> > + if (!pasid_valid(min) || !pasid_valid(max) ||
> > + min == 0 || max < min)
>
> No need to change above line.
>
> > return -EINVAL;
> >
> > mutex_lock(&iommu_sva_lock);
> > /* Is a PASID already associated with this mm? */
> > if (pasid_valid(mm->pasid)) {
> > - if (mm->pasid < min || mm->pasid >= max)
> > + if (mm->pasid < min || mm->pasid > max)
>
> I forgot why do we need to change above line. But it's better to put
> some comments there so that people don't need to dive into
> ioasid_alloc() to know the inclusion or exclusion of @min or @max.
>
just to be consistent for both limits. sure, we can add the comment.
> > ret = -EOVERFLOW;
> > goto out;
> > }
> >
> > - pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
> > - if (!pasid_valid(pasid))
> > - ret = -ENOMEM;
> > - else
> > - mm->pasid = pasid;
> > + ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
> > GFP_ATOMIC);
> > + if (ret < 0)
> > + goto out;
> > + mm->pasid = ret;
> > + ret = 0;
> > out:
> > mutex_unlock(&iommu_sva_lock);
> > return ret;
> > }
> > -EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
> >
> > /**
> > * iommu_sva_bind_device() - Bind a process address space to a device
> > @@ -221,8 +207,8 @@ iommu_sva_handle_iopf(struct iommu_fault *fault,
> > void *data)
> > void mm_pasid_drop(struct mm_struct *mm)
> > {
> > - if (pasid_valid(mm->pasid)) {
> > - ioasid_free(mm->pasid);
> > - mm->pasid = INVALID_IOASID;
> > - }
> > + if (likely(!pasid_valid(mm->pasid)))
> > + return;
> > +
> > + ida_free(&iommu_global_pasid_ida, mm->pasid);
>
> Any reason why do you drop "mm->pasid = INVALID_IOASID;" here?
>
mm_drop is called when mm gets released because "mm_count" becomes zero. so
there is no more mm_users. No one will see mm->pasid after this.
On the other hand, iommu_sva_bind_device() needs to hold mm_users refcount
so it won;t happen after mm_drop.
> > }
> > diff --git a/drivers/iommu/iommu-sva.h b/drivers/iommu/iommu-sva.h
> > index 102eae1817a2..c22d0174ad61 100644
> > --- a/drivers/iommu/iommu-sva.h
> > +++ b/drivers/iommu/iommu-sva.h
> > @@ -8,8 +8,6 @@
> > #include <linux/ioasid.h>
> > #include <linux/mm_types.h>
> >
> > -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t
> > max); -
> > /* I/O Page fault */
> > struct device;
> > struct iommu_fault;
>
> Best regards,
> baolu
Thanks,
Jacob
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