On 2023/3/24 21:18, Baoquan He wrote: > Problem: > ======= > On arm64, block and section mapping is supported to build page tables. > However, currently it enforces to take base page mapping for the whole > linear mapping if CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is enabled and > crashkernel kernel parameter is set. This will cause longer time of the > linear mapping process during bootup and severe performance degradation > during running time. > > Root cause: > ========== > On arm64, crashkernel reservation relies on knowing the upper limit of > low memory zone because it needs to reserve memory in the zone so that > devices' DMA addressing in kdump kernel can be satisfied. However, the > upper limit of low memory on arm64 is variant. And the upper limit can > only be decided late till bootmem_init() is called [1]. > > And we need to map the crashkernel region with base page granularity when > doing linear mapping, because kdump needs to protect the crashkernel region > via set_memory_valid(,0) after kdump kernel loading. However, arm64 doesn't > support well on splitting the built block or section mapping due to some > cpu reststriction [2]. And unfortunately, the linear mapping is done before > bootmem_init(). > > To resolve the above conflict on arm64, the compromise is enforcing to > take base page mapping for the entire linear mapping if crashkernel is > set, and CONFIG_ZONE_DMA or CONFIG_ZONE_DMA32 is enabed. Hence > performance is sacrificed. > > Solution: > ========= > Comparing with the base page mapping for the whole linear region, it's > better to take off the protection on crashkernel memory region for the > time being because the anticipated stamping on crashkernel memory region > could only happen in a chance in one million, while the base page mapping > for the whole linear region is mitigating arm64 systems with crashkernel > set always. > > [1] > https://lore.kernel.org/all/YrIIJkhKWSuAqkCx@xxxxxxx/T/#u > > [2] > https://lore.kernel.org/linux-arm-kernel/20190911182546.17094-1-nsaenzjulienne@xxxxxxx/T/ > > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx> > --- > arch/arm64/include/asm/kexec.h | 6 ------ > arch/arm64/kernel/machine_kexec.c | 20 -------------------- > 2 files changed, 26 deletions(-) > > diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h > index 559bfae26715..9ac9572a3bbe 100644 > --- a/arch/arm64/include/asm/kexec.h > +++ b/arch/arm64/include/asm/kexec.h > @@ -102,12 +102,6 @@ void cpu_soft_restart(unsigned long el2_switch, unsigned long entry, > > int machine_kexec_post_load(struct kimage *image); > #define machine_kexec_post_load machine_kexec_post_load > - > -void arch_kexec_protect_crashkres(void); > -#define arch_kexec_protect_crashkres arch_kexec_protect_crashkres > - > -void arch_kexec_unprotect_crashkres(void); > -#define arch_kexec_unprotect_crashkres arch_kexec_unprotect_crashkres > #endif > > #define ARCH_HAS_KIMAGE_ARCH > diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c > index ce3d40120f72..22da7fc1ff50 100644 > --- a/arch/arm64/kernel/machine_kexec.c > +++ b/arch/arm64/kernel/machine_kexec.c > @@ -268,26 +268,6 @@ void machine_crash_shutdown(struct pt_regs *regs) > pr_info("Starting crashdump kernel...\n"); > } > > -void arch_kexec_protect_crashkres(void) > -{ > - int i; > - > - for (i = 0; i < kexec_crash_image->nr_segments; i++) > - set_memory_valid( > - __phys_to_virt(kexec_crash_image->segment[i].mem), > - kexec_crash_image->segment[i].memsz >> PAGE_SHIFT, 0); > -} > - > -void arch_kexec_unprotect_crashkres(void) > -{ > - int i; > - > - for (i = 0; i < kexec_crash_image->nr_segments; i++) > - set_memory_valid( > - __phys_to_virt(kexec_crash_image->segment[i].mem), > - kexec_crash_image->segment[i].memsz >> PAGE_SHIFT, 1); > -} > - > #ifdef CONFIG_HIBERNATION > /* > * To preserve the crash dump kernel image, the relevant memory segments > Reviewed-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx> -- Regards, Zhen Lei _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
