Date: Sun, 24 Feb 2019 10:27:26 +0100 From: =?UTF-8?B?VMSzbA==?= Coosemans <tijl@FreeBSD.org> To: Steve Kargl <sgk@troutmask.apl.washington.edu> Cc: Warner Losh <imp@bsdimp.com>, Konstantin Belousov <kostikbel@gmail.com>, FreeBSD Current <freebsd-current@freebsd.org>, Peter Holm <pho@freebsd.org>, Mark Johnston <markj@freebsd.org> Subject: Re: r343567 aka PAE vs non-PAE merge breaks i386 freebsd Message-ID: <20190224102726.746adb9f@kalimero.tijl.coosemans.org> In-Reply-To: <20190224012851.GA21748@troutmask.apl.washington.edu> References: <20190222033924.GA25285@troutmask.apl.washington.edu> <20190222060410.GA25817@troutmask.apl.washington.edu> <20190223032644.GA14058@troutmask.apl.washington.edu> <20190223091931.GE2420@kib.kiev.ua> <20190223163619.GA18805@troutmask.apl.washington.edu> <CANCZdfpnpMLpLs2BCBvrBTfFxTx8B8MMDoWAh4xE_4Ge0LRSVA@mail.gmail.com> <20190224012851.GA21748@troutmask.apl.washington.edu>
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On Sat, 23 Feb 2019 17:28:51 -0800 Steve Kargl <sgk@troutmask.apl.washington.edu> wrote: > On Sat, Feb 23, 2019 at 12:03:58PM -0700, Warner Losh wrote: >> On Sat, Feb 23, 2019 at 10:57 AM Steve Kargl >> <sgk@troutmask.apl.washington.edu> wrote: >>> Supposely, the laptop only has 4 GB of memory. Not sure how >>> it finds memory above 4 GB. >> >> Some older chipsets had a 'hole' in memory that they mapped the PCI bus >> into and then remapped RAM in that range up above the 4GB boundary. That's >> how it can find memory above 4GB when you have only 4GB of RAM. I hit it >> with the PC Card stuff I did back in the day since it broke certain >> heuristics I had in the code that turned out to be unwise for many reasons >> (not just this one). I don't recall all the details, since it's been so >> long ago. >> >> So I think kib@ is right when he highlights >>> +0x0000000100000000 - 0x000000011ffe7fff, 536772608 bytes (131048 pages) >> >> as the memory, since this is indeed above the 4GB limit. It's about 128k >> of 4k pages (just shy of the 131072 I'd expect), which is a surprisingly >> round number. Also one that's easy to implement in hardware. So it >> certainly "smells" the same... >> >> That's why I agree with others that hw.above4g_allow=0 is worth a shot, for >> at least diagnostic purposes. This memory wasn't used before and if it's >> used now by the drm drivers, and those aren't PAE safe (meaning they cope >> with allocations beyond 4GB), then that's quite useful to know. Or maybe >> it's a different driver hating things and stomping on video memory due to >> wrap around. > > Thanks for the explanation. Here's an update. TL;DR: xorg is > up and running; drm-legacy-kmod seems to be unsafe/unaware of > PAE. > > Build world/kernel, drm-legacy-kmod, minimum needed ports for xorg. > Kernel is unmodified GENERIC. > > Reboot without setting anything in /boot/loader.conf > > % sysctl -a | grep above > % sysctl -a | grep pae > vm.pmap.pae_mode: 1 > % kldload /boot/modules/i915kms.ko > > Black screen of death. Did not even get to running xinit. > > Hard reset to single user mode. > > # fsck -y > # mount -a > # vi /boot/loader.conf. > (Add hw.above4g_allow=0) > # sync > # shutdown -r now > > % sysctl -a | grep above > % sysctl -a | grep pae > vm.pmap.pae_mode: 1 > % cat /boot/loader.conf > if_ath_load="YES" > if_ath_pci_load="YES" > cpuctl_load="YES" > hw.above4g_allow=0 > % kldload /boot/modules/i915kms.ko > > Switch to vt3, login as normal user. > > % startx -- -depth 24 >& ~/tmp/.x.out > > Xorg is up and running. Not sure why my first attempt at using > hw.above4g_allow=0 did not work. Perhaps, mismatch between the xorg > bits and kernel/world bits. > > % sysctl -a | grep mem > vm.lowmem_period: 10 > vm.kmem_map_free: 1669365760 > vm.kmem_map_size: 41910272 > vm.kmem_size_scale: 1 > vm.kmem_size_max: 1711276032 > vm.kmem_size_min: 12582912 > vm.kmem_zmax: 65536 > vm.kmem_size: 1711276032 > hw.physmem: 3715489792 > hw.usermem: 3592175616 > hw.realmem: 4294963200 > > % dmesg | grep memory > real memory = 4294967296 (4096 MB) > avail memory = 3637673984 (3469 MB) > agp0: aperture size is 256M, detected 7676k stolen memory > > The pre-r343567 dmesg has > > real memory = 4294967296 (4096 MB) > avail memory = 3639914496 (3471 MB) > > I can live with 2 MB loss. > > Conclusion, drm-legacy-kmod is not PAE safe/aware. > > Probably want to put something in /usr/src about possible > problems with new pmap.h on i386 FreeBSD. Now it would be interesting to do the same tests with drm-current-kmod.
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