From mboxrd@z Thu Jan 1 00:00:00 1970 From: hdegoede@redhat.com (Hans de Goede) Date: Tue, 28 Apr 2015 12:05:37 +0200 Subject: [REGRESSION?] ARM: 7677/1: LPAE: Fix mapping in alloc_init_section for unaligned addresses (was Re: Memory size unaligned to section boundary) In-Reply-To: References: Message-ID: <553F5B71.8030309@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi all, On 23-04-15 15:19, Stefan Agner wrote: > Hi, > > It seems to me that I hit an issue in low memory mapping (map_lowmem). > I'm using a custom memory size, which leads to an freeze on Linux 4.0 > and also with Linus master on two tested ARMv7-A SoC's (Freescale Vybrid > and NVIDIA Tegra 3): > > With mem=259744K > [ 0.000000] Booting Linux on physical CPU 0x0 > [ 0.000000] Linux version 4.0.0-00189-ga4d2a4c3-dirty > (ags at trochilidae) (gcc version 4.8.3 20140401 (prerelease) (Linaro GCC > 4.8-2014.04) ) #506 Thu Apr 23 14:13:21 CEST 2015 > [ 0.000000] CPU: ARMv7 Processor [410fc051] revision 1 (ARMv7), > cr=10c5387d > [ 0.000000] CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing > instruction cache > [ 0.000000] Machine model: Toradex Colibri VF61 on Colibri Evaluation > Board > [ 0.000000] bootconsole [earlycon0] enabled > [ 0.000000] cma: Reserved 16 MiB at 0x8e400000 > [ 0.000000] Memory policy: Data cache writeback > > > I dug a bit more into that, and it unveiled that when creating the > mapping for the non-kernel_x part (if (kernel_x_end < end) in > map_lowmem), the unaligned section at the end leads to the freeze. In > alloc_init_pmd, if the memory end is section unaligned, alloc_init_pte > gets called which allocates a PTE outside of the initialized region (in > early_alloc_aligned). The system freezes at the call of memset in > early_alloc_aligned function. > > With some debug print, this can be better illustrated: > [ 0.000000] pgd 800063f0, addr 8fc00000, end 8fda8000, next 8fda8000 > [ 0.000000] pud 800063f0, addr 8fc00000, end 8fda8000, next 8fda8000 > [ 0.000000] pmd 800063f0, addr 8fc00000, next 8fda8000 > => actual end of memory ^^^^^^^^ > [ 0.000000] alloc_init_pte > [ 0.000000] set_pte_ext, pte 00000000, addr 8fc00000, end 8fda8000 > [ 0.000000] early_pte_alloc > [ 0.000000] early_alloc_aligned, 00001000, ptr 8fcff000, align > 00001000 > => PTE allocated outside of initialized area ^^^^^^^^ > > It seems that memory gets allocation in the last section. When the last > section was in the previous PMD, the allocation works, however if the > last section is within the same PMD, the allocation ends up in the > non-initialized area. So: > > In other words, sizes which end in a upper part of the 2MB sized PMD > fail, while sizes in the lower part of a PMD work. > 0xFF80000 => fails (mem=261632K) > 0xFE80000 => works (mem=260608K) > 0xFD80000 => fails (mem=261632K) > ... > > While I understand the reason for the freeze, I don't know to properly > fix it. It looks to me that in alloc_init_pmd, we should use > __map_init_section first to map the last aligned section, before calling > alloc_init_pte on the non aligned section. > > Background: I tried to reuse the boot loader part of the simplefb > implementation for sunxi. It decreases memory size by the size of the > framebuffer. Hence the actually memory size can be unaligned, depending > on the display size used. In the case at hand, a framebuffer of the size > 800x600 worked while 1024x600 did not work... The implementation uses > device tree to report the memory size, but the kernel arguments show the > same behavior. > > Maybe a regression of e651eab0af ("ARM: 7677/1: LPAE: Fix mapping in > alloc_init_section for unaligned addresses"). I currently do not have a > platform at hand which works on that Linux version out of the box. I'm seeing this to an Allwinner Cortex A7 based SoCs, specifically on tablets with a 1024x600 lcd screen it seems that shaving exactly the amount of memory needed for a 32bpp 1024x600 framebuffer of from the top of memory triggers this. Regards, Hans