Messages in this thread | | | Date | Tue, 12 Jul 2022 20:14:45 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCHv4 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR |
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On Tue, Jul 12, 2022 at 03:12:01PM +0200, Alexander Potapenko wrote: > On Wed, Jun 22, 2022 at 6:22 PM Kirill A. Shutemov > <kirill.shutemov@linux.intel.com> wrote: > > > > Add a couple of arch_prctl() handles: > > > > - ARCH_ENABLE_TAGGED_ADDR enabled LAM. The argument is required number > > of tag bits. It is rounded up to the nearest LAM mode that can > > provide it. For now only LAM_U57 is supported, with 6 tag bits. > > > > - ARCH_GET_UNTAG_MASK returns untag mask. It can indicates where tag > > bits located in the address. > > > Am I right that the desired way to detect the presence of LAM without > enabling it is to check that arch_prctl(ARCH_GET_UNTAG_MASK, ...) > returns zero?
Returns -1UL, but yes.
> Overall, I think these new arch_prctls should be documented following > the spirit of PR_SET_TAGGED_ADDR_CTRL/PR_GET_TAGGED_ADDR_CTRL > somewhere.
The plan is to update man page for the syscall once the interface is upstream.
> > + > > +static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits) > > +{ > > + int ret = 0; > > + > > + if (!cpu_feature_enabled(X86_FEATURE_LAM)) > > + return -ENODEV; > > + > > + mutex_lock(&mm->context.lock); > > + > > + /* Already enabled? */ > > + if (mm->context.lam_cr3_mask) { > > + ret = -EBUSY; > > + goto out; > > + } > > + > > + if (!nr_bits) { > > + ret = -EINVAL; > > One would expect that `arch_prctl(ARCH_ENABLE_TAGGED_ADDR, 0)` > disables tagging for the current process. > Shouldn't this workflow be supported as well?
Is there an use-case for it?
I would rather keep the interface minimal. We can always add this in the future if an use-case comes.
-- Kirill A. Shutemov
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