Date: Sat, 23 Feb 2019 17:28:51 -0800 From: Steve Kargl <sgk@troutmask.apl.washington.edu> To: Warner Losh <imp@bsdimp.com> Cc: 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: <20190224012851.GA21748@troutmask.apl.washington.edu> In-Reply-To: <CANCZdfpnpMLpLs2BCBvrBTfFxTx8B8MMDoWAh4xE_4Ge0LRSVA@mail.gmail.com> 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>
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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. > > Warner 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. -- Steve
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