From: Fenghua Yu <fenghua.yu@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Peter Zijlstra <peterz@infradead.org>,
Andy Lutomirski <luto@kernel.org>,
Tony Luck <tony.luck@intel.com>,
Lu Baolu <baolu.lu@linux.intel.com>,
Joerg Roedel <joro@8bytes.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Ashok Raj <ashok.raj@intel.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
iommu@lists.linux-foundation.org, x86 <x86@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 04/11] kernel/fork: Initialize mm's PASID
Date: Fri, 4 Feb 2022 16:25:34 -0800 [thread overview]
Message-ID: <Yf3D/ij6S8AbMwpF@otcwcpicx3.sc.intel.com> (raw)
In-Reply-To: <87wniab4kb.ffs@tglx>
Hi, Thomas,
On Sat, Feb 05, 2022 at 12:22:12AM +0100, Thomas Gleixner wrote:
> On Fri, Jan 28 2022 at 12:28, Fenghua Yu wrote:
> > A new mm doesn't have a PASID yet when it's created. Initialize
> > the mm's PASID on fork() or for init_mm to INVALID_IOASID (-1).
>
> I must be missing something here.
>
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index aa5f09ca5bcf..c74d1edbac2f 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -8,6 +8,7 @@
> > #include <linux/mm_types.h>
> > #include <linux/gfp.h>
> > #include <linux/sync_core.h>
> > +#include <linux/ioasid.h>
> >
> > /*
> > * Routines for handling mm_structs
> > @@ -433,4 +434,13 @@ static inline void membarrier_update_current_mm(struct mm_struct *next_mm)
> > }
> > #endif
> >
> > +#ifdef CONFIG_IOMMU_SVA
> > +static inline void mm_pasid_init(struct mm_struct *mm)
> > +{
> > + mm->pasid = INVALID_IOASID;
> > +}
> > +#else
> > +static inline void mm_pasid_init(struct mm_struct *mm) {}
> > +#endif
> > +
> > #endif /* _LINUX_SCHED_MM_H */
>
> So this adds mm_pasid_init() to linux/sched/mm.h which replaces:
>
> > -static void mm_init_pasid(struct mm_struct *mm)
> > -{
> > -#ifdef CONFIG_IOMMU_SVA
> > - mm->pasid = INIT_PASID;
> > -#endif
> > -}
> > -
>
> I.e. already existing code which is initializing mm->pasid with
> INIT_PASID (0) while the replacement initializes it with INVALID_IOASID
> (-1).
>
> The change log does not have any information about why INIT_PASID is the
> wrong initialization value and why this change is not having any side
> effects.
I should add the following info in the commit message to explain why
change INIT_PASID (0) to INVALID_IOASID (-1):
INIT_PASID (0) is reserved for kernel legacy DMA PASID. It cannot be
allocated to a user process. Initialize the process's PASID to 0 may
cause confusion that why the process uses reserved kernel legacy DMA
PASID. Initializing the PASID to INVALID_IOASID (-1) explicitly
tells the process doesn't have a valid PASID yet initially.
Is it OK for you?
>
> It neither mentions why having this in a global available header makes
> sense when the only call site is in the C file from which the already
> existing function is removed.
This series defines three helpers mm_pasid_init(), mm_pasid_set(), and
mm_pasid_drop() in mm because they handle the pasid member in mm_struct
and should be part of mm operations. I explained why mm_pasid_set() and
mm_pasid_drop() are defined in mm, but I didn't explain why mm_pasid_init()
is define in mm.
Is it OK to add the following explanation on why mm_pasid_init() is defined?
mm_pasid_init() is defined in mm and replaces mm_init_pasid() because
the PASID init operation initializes the pasid member in mm_struct and
should be part of mm operations.
Thanks,
-Fenghua
next prev parent reply other threads:[~2022-02-05 0:25 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-28 20:28 [PATCH v3 00/11] Re-enable ENQCMD and PASID MSR Fenghua Yu
2022-01-28 20:28 ` [PATCH v3 01/11] iommu/sva: Rename CONFIG_IOMMU_SVA_LIB to CONFIG_IOMMU_SVA Fenghua Yu
2022-02-04 23:07 ` Thomas Gleixner
2022-01-28 20:28 ` [PATCH v3 02/11] mm: Change CONFIG option for mm->pasid field Fenghua Yu
2022-02-04 23:07 ` Thomas Gleixner
2022-01-28 20:28 ` [PATCH v3 03/11] iommu/ioasid: Introduce a helper to check for valid PASIDs Fenghua Yu
2022-02-04 23:08 ` Thomas Gleixner
2022-02-04 23:23 ` Thomas Gleixner
2022-01-28 20:28 ` [PATCH v3 04/11] kernel/fork: Initialize mm's PASID Fenghua Yu
2022-02-04 23:22 ` Thomas Gleixner
2022-02-05 0:25 ` Fenghua Yu [this message]
2022-01-28 20:28 ` [PATCH v3 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit Fenghua Yu
2022-02-04 23:56 ` Thomas Gleixner
2022-02-05 0:33 ` Fenghua Yu
2022-02-05 3:50 ` Lu Baolu
2022-02-05 5:10 ` Fenghua Yu
2022-02-05 7:10 ` Lu Baolu
2022-01-28 20:29 ` [PATCH v3 06/11] x86/fpu: Clear PASID when copying fpstate Fenghua Yu
2022-02-04 23:58 ` Thomas Gleixner
2022-01-28 20:29 ` [PATCH v3 07/11] sched: Define and initialize a flag to identify valid PASID in the task Fenghua Yu
2022-02-04 23:58 ` Thomas Gleixner
2022-01-28 20:29 ` [PATCH v3 08/11] x86/traps: Demand-populate PASID MSR via #GP Fenghua Yu
2022-02-05 0:00 ` Thomas Gleixner
2022-01-28 20:29 ` [PATCH v3 09/11] x86/cpufeatures: Re-enable ENQCMD Fenghua Yu
2022-02-05 0:00 ` Thomas Gleixner
2022-01-28 20:29 ` [PATCH v3 10/11] tools/objtool: Check for use of the ENQCMD instruction in the kernel Fenghua Yu
2022-01-28 20:29 ` [PATCH v3 11/11] docs: x86: Change documentation for SVA (Shared Virtual Addressing) Fenghua Yu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Yf3D/ij6S8AbMwpF@otcwcpicx3.sc.intel.com \
--to=fenghua.yu@intel.com \
--cc=ashok.raj@intel.com \
--cc=baolu.lu@linux.intel.com \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=iommu@lists.linux-foundation.org \
--cc=jacob.jun.pan@linux.intel.com \
--cc=joro@8bytes.org \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=ravi.v.shankar@intel.com \
--cc=tglx@linutronix.de \
--cc=tony.luck@intel.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).