Re: kern/54994: Critical bug in uarea_poolpage_alloc() for archs with __HAVE_CPU_UAREA_ROUTINES

[Nick Hudson <nick.hudson%gmx.co.uk@localhost>]

The following reply was made to PR kern/54994; it has been noted by GNATS.

From: Nick Hudson <nick.hudson%gmx.co.uk@localhost>
To: Rin Okuyama <rokuyama.rk%gmail.com@localhost>, Jason Thorpe <thorpej%me.com@localhost>
Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 netbsd-bugs%netbsd.org@localhost, gnats-bugs%netbsd.org@localhost
Subject: Re: kern/54994: Critical bug in uarea_poolpage_alloc() for archs with
 __HAVE_CPU_UAREA_ROUTINES
Date: Tue, 25 Feb 2020 12:38:44 +0000

 On 25/02/2020 11:24, Rin Okuyama wrote:
 > On 2020/02/24 9:29, Rin Okuyama wrote:
 >> __HAVE_CPU_UAREA_ROUTINES is enabled for alpha, mips,
 >> powerpc/{oae,ibm4xx,booke}, and riscv. I investigated whether it is
 >> really necessary or not for these archs (except for riscv).
 >>
 >> In short, most of these archs do *not* need direct-mapped physically
 >> contiguous u-area for now, as far as I can see (source code reading
 >> and experiment on powerpc/oea, just experiment on other archs). Only
 >> the exception is powerpc/ibm4xx, which should also be fixed.
 >>
 >> So is it time to retire __HAVE_CPU_UAREA_ROUTINES?
 >
 > Oops, mips64 depends on direct-mapped u-area (with UPAGES =3D=3D 1);
 > KASSERT fires on ERLITE (MIPS64_OCTEON) if __HAVE_CPU_UAREA_ROUTINES
 > is turned off:
 
 On mips64 iirc it's architecturally defined to have direct-map,
 i.e. XKPHYS, so the fallback from cpu_uarea_alloc to
 uvm_km_alloc "should" never happen.
 
 This conditional is also slightly off I think
 
 http://src.illumos.org/source/xref/netbsd-src/sys/uvm/uvm_glue.c#247
 
 247	while (USPACE =3D=3D PAGE_SIZE && USPACE_ALIGN =3D=3D 0) {
 
 the following is more correct (imo)
 
 	while (USPACE =3D=3D PAGE_SIZE &&
 	    (USPACE_ALIGN =3D=3D 0 || USPACE_ALIGN =3D=3D PAGE_SIZE)) {
 
 
 All that said I'm facing my own issues with uvm_pglistalloc not waiting
 for > PAGE_SIZE physically contiguous allocations (2 pages in my case)
 
 Nick