linux-kernel - Re: [PATCH 5/7] x86/mmu: Allocate/free PASID

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Message-ID: <20200427221825.GF242333@romley-ivt3.sc.intel.com>
Date:   Mon, 27 Apr 2020 15:18:25 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Jacob Jun Pan <jacob.jun.pan@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, iommu@...ts.linux-foundation.org
Subject: Re: [PATCH 5/7] x86/mmu: Allocate/free PASID

On Sun, Apr 26, 2020 at 04:55:25PM +0200, Thomas Gleixner wrote:
> Fenghua Yu <fenghua.yu@...el.com> writes:
> > +++ b/arch/x86/include/asm/mmu.h @@ -50,6 +50,10 @@ typedef struct {
> >  	u16 pkey_allocation_map; s16 execute_only_pkey;
> >  #endif
> > + +#ifdef CONFIG_INTEL_IOMMU_SVM +	int pasid;
> 
> int? It's a value which gets programmed into the MSR along with the valid 
> bit (bit 31) set.

The pasid is defined as "int" in struct intel_svm and in 
intel_svm_bind_mm() and intel_svm_unbind_mm(). So the pasid defined in this 
patch follows the same type defined in those places.

But as you pointed out below, ioasid_t is defined as "unsigned int".

> 
> >  extern void switch_mm(struct mm_struct *prev, struct mm_struct *next, 
> > diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c 
> > index d7f2a5358900..da718a49e91e 100644 --- a/drivers/iommu/intel-svm.c 
> > +++ b/drivers/iommu/intel-svm.c @@ -226,6 +226,45 @@ static 
> > LIST_HEAD(global_svm_list);
> >  	list_for_each_entry((sdev), &(svm)->devs, list)	\
> >  		if ((d) != (sdev)->dev) {} else
> >  
> > +/* + * If this mm already has a PASID we can use it. Otherwise 
> > allocate a new one. + * Let the caller know if we did an allocation via 
> > 'new_pasid'. + */ +static int alloc_pasid(struct intel_svm *svm, struct 
> > mm_struct *mm, + int pasid_max, bool *new_pasid, int flags)
> 
> Again, data types please. flags are generally unsigned and not plain int. 
> Also pasid_max is certainly not plain int either.

The caller defines pasid_max and flags as "int". This function just follows
the caller's definitions.

But I will change their definitions to "unsigned int" here.

> 
> > + *new_pasid = false; + + return mm->context.pasid; + } + + /* + * 
> > Allocate a new pasid. Do not use PASID 0, reserved for RID to + * 
> > PASID. + */ + pasid = ioasid_alloc(NULL, PASID_MIN, pasid_max - 1, 
> > svm);
> 
> ioasid_alloc() uses ioasid_t which is
> 
> typedef unsigned int ioasid_t;
> 
> Can we please have consistent types and behaviour all over the place?

Should I just define "pasid", "pasid_max", "flags" as "unsigned int" for
the new functions/code?

Or should I also change their types to "unsigned int" in the original
svm code (struct intel_svm, ...bind_mm(), etc)? I'm afraid that will be
a lot of changes and should be in a separate preparation patch.

Thanks.

-Fenghua