Subject: Re: [PATCH] iommu: Allow device driver to use its own PASID space for SVA

From: Joonwon Kang <[email-masked]>
Date: Tue, 19 May 2026 08:11:47 +0000

> On Mon, May 18, 2026 at 09:06:54AM +0000, Joonwon Kang wrote:
> > > On Fri, May 15, 2026 at 09:46:05AM +0000, Joonwon Kang wrote:
> > > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> > > > index 0ca3912ecb7f..61e2e52105e5 100644
> > > > --- a/arch/x86/kernel/traps.c
> > > > +++ b/arch/x86/kernel/traps.c
> > > > @@ -864,6 +864,8 @@ static bool try_fixup_enqcmd_gp(void)
> > > >  		return false;
> > > >  
> > > >  	pasid = mm_get_enqcmd_pasid(current->mm);
> > > > +	if (pasid == IOMMU_PASID_INVALID)
> > > > +		return false;
> > > 
> > > If you do this then probably you should get rid of mm_valid_pasid(),
> > > mm_get_enqcmd_pasid() already has the NULL check so the two functions
> > > are kind of pointless.
> > > 
> > > You also missed the other place calling mm_valid_pasid() that should
> > > really be sensitive to this as well:
> > > 
> > > static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
> > > {
> > > [..]
> > >         if (mm_valid_pasid(mm) &&
> > >             !test_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &mm->context.flags))
> > >                 return -EINVAL;
> > > 
> > > Make that removal a prep patch
> > > 
> > 
> > Thanks for pointing this out. I think mm_valid_pasid() is to check if SVA
> > is currently in action while mm_get_enqcmd_pasid() is to get the PASID for
> > "ENQCMD instruction execution".
> 
> > Since it is now possible with this patch to activate SVA without involving
> > EL0(for ENQCMD-like instructions),
> 
> I see, this thing about which is about LAM should remain, yes
> 
> But all the "EL0" machinery about trapping and enabling ENQCMD should
> be moved over to mm_get_enqcmd_pasid() and never call mm_valid_pasid()

Yes, it makes sense. Let me fix that in the next version.

Thanks,
Joonwon Kang