| Message ID | 20150506101104.GD2067@n2100.arm.linux.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Russell, On Wed, May 06, 2015 at 11:11:05AM +0100, Russell King - ARM Linux wrote: > On Thu, Apr 23, 2015 at 03:19:45PM +0200, 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@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 > > <freeze> > > > > 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 ^^^^^^^^ > > Right, and the question is why does that happen - and the answer is > this: > > /* > * Round the memblock limit down to a section size. This > * helps to ensure that we will allocate memory from the > * last full section, which should be mapped. > */ > if (memblock_limit) > memblock_limit = round_down(memblock_limit, SECTION_SIZE); > > That should round down by 2x SECTION_SIZE to ensure that we don't start > allocating the L2 page table in a section which isn't mapped. Please > try this patch: > > arch/arm/mm/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c > index 4e6ef896c619..387becac5c86 100644 > --- a/arch/arm/mm/mmu.c > +++ b/arch/arm/mm/mmu.c > @@ -1142,7 +1142,7 @@ void __init sanity_check_meminfo(void) > * last full section, which should be mapped. > */ > if (memblock_limit) > - memblock_limit = round_down(memblock_limit, SECTION_SIZE); > + memblock_limit = round_down(memblock_limit, 2 * SECTION_SIZE); > if (!memblock_limit) > memblock_limit = arm_lowmem_limit; For LPAE, where SECTION_SIZE == PMD_SIZE, this will set the memblock limit a section lower than necessary. In another subthread thread [1] I suggested roudning down to PMD_SIZE instead, which should do the right thing regardless of LPAE. Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/340925.html
On Wed, May 06, 2015 at 11:11:05AM +0100, Russell King - ARM Linux wrote: > On Thu, Apr 23, 2015 at 03:19:45PM +0200, Stefan Agner wrote: > > 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. [...] > Right, and the question is why does that happen - and the answer is > this: > > /* > * Round the memblock limit down to a section size. This > * helps to ensure that we will allocate memory from the > * last full section, which should be mapped. > */ > if (memblock_limit) > memblock_limit = round_down(memblock_limit, SECTION_SIZE); > > That should round down by 2x SECTION_SIZE to ensure that we don't start > allocating the L2 page table in a section which isn't mapped. Please > try this patch: > > arch/arm/mm/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c > index 4e6ef896c619..387becac5c86 100644 > --- a/arch/arm/mm/mmu.c > +++ b/arch/arm/mm/mmu.c > @@ -1142,7 +1142,7 @@ void __init sanity_check_meminfo(void) > * last full section, which should be mapped. > */ > if (memblock_limit) > - memblock_limit = round_down(memblock_limit, SECTION_SIZE); > + memblock_limit = round_down(memblock_limit, 2 * SECTION_SIZE); Why not PMD_SIZE? We don't need 4MB round down with LPAE.
On Wed, May 06, 2015 at 11:51:03AM +0100, Catalin Marinas wrote: > On Wed, May 06, 2015 at 11:11:05AM +0100, Russell King - ARM Linux wrote: > > @@ -1142,7 +1142,7 @@ void __init sanity_check_meminfo(void) > > * last full section, which should be mapped. > > */ > > if (memblock_limit) > > - memblock_limit = round_down(memblock_limit, SECTION_SIZE); > > + memblock_limit = round_down(memblock_limit, 2 * SECTION_SIZE); > > Why not PMD_SIZE? We don't need 4MB round down with LPAE. No reason - PMD_SIZE would be good there.
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c index 4e6ef896c619..387becac5c86 100644 --- a/arch/arm/mm/mmu.c +++ b/arch/arm/mm/mmu.c @@ -1142,7 +1142,7 @@ void __init sanity_check_meminfo(void) * last full section, which should be mapped. */ if (memblock_limit) - memblock_limit = round_down(memblock_limit, SECTION_SIZE); + memblock_limit = round_down(memblock_limit, 2 * SECTION_SIZE); if (!memblock_limit) memblock_limit = arm_lowmem_limit;