On Thu, Jul 14, 2022 at 04:28:36PM +0200, Alexander Potapenko wrote: > On Tue, Jul 12, 2022 at 7:14 PM Kirill A. Shutemov > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > > 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@xxxxxxxxxxxxxxx> 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. > > No, I meant the return value of arch_prctl(), but in fact neither > seems to be true. > > Right now e.g. for the 5.17 kernel arch_prctl(ARCH_GET_UNTAG_MASK, > &bits) returns -EINVAL regardless of the underlying hardware. > A new kernel with your patches will return 0 and set bits=-1UL on both > non-LAM and LAM-enabled machines. How can we distinguish those? With CPUID? -- Kirill A. Shutemov
