linux-kernel - Re: [PATCHv8 00/11] Linear Address Masking enabling

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Date:   Mon, 12 Sep 2022 13:39:35 -0700
From:   Jacob Pan <jacob.jun.pan@...el.com>
To:     Ashok Raj <ashok_raj@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>, <x86@...nel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Ashok Raj <ashok.raj@...el.com>, jacob.jun.pan@...el.com
Subject: Re: [PATCHv8 00/11] Linear Address Masking enabling

Hi Ashok,

On Fri, 9 Sep 2022 16:08:02 +0000, Ashok Raj <ashok_raj@...ux.intel.com>
wrote:

> > diff --git a/arch/x86/include/uapi/asm/prctl.h
> > b/arch/x86/include/uapi/asm/prctl.h index a31e27b95b19..e5c04ced36c9
> > 100644 --- a/arch/x86/include/uapi/asm/prctl.h
> > +++ b/arch/x86/include/uapi/asm/prctl.h
> > @@ -23,5 +23,6 @@
> >  #define ARCH_GET_UNTAG_MASK		0x4001
> >  #define ARCH_ENABLE_TAGGED_ADDR		0x4002
> >  #define ARCH_GET_MAX_TAG_BITS		0x4003
> > +#define ARCH_ENABLE_TAGGED_ADDR_FORCED	0x4004
> >  
> >  #endif /* _ASM_X86_PRCTL_H */
> > diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> > index 337f80a0862f..7d89a2fd1a55 100644
> > --- a/arch/x86/kernel/process_64.c
> > +++ b/arch/x86/kernel/process_64.c
> > @@ -774,7 +774,8 @@ static bool lam_u48_allowed(void)
> >  #define LAM_U48_BITS 15
> >  #define LAM_U57_BITS 6
> >  
> > -static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned
> > long nr_bits) +static int prctl_enable_tagged_addr(struct mm_struct
> > *mm, unsigned long nr_bits,
> > +				    bool forced)
> >  {
> >  	int ret = 0;
> >  
> > @@ -793,6 +794,11 @@ static int prctl_enable_tagged_addr(struct
> > mm_struct *mm, unsigned long nr_bits) goto out;
> >  	}
> >  
> > +	if (pasid_valid(mm->pasid) && !forced) {
I don't think this works since we have lazy pasid free.  for example,
after all the devices did sva_unbind, mm->pasid  we'll remain valid until
mmdrop(). LAM  should be supported in this case.

Perhaps, we could introduce another prctl flag for SVA, PR_GET_SVA?
Both iommu driver and LAM can set/query the flag. LAM applications may not
be the only ones want to know if share virtual addressing is  on.

> > +		ret = -EBUSY;
> > +		goto out;
> > +	}
> > +

Thanks,

Jacob