Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> writes:
> Hi Björn,
>
> On Tue, May 14, 2024 at 4:05 PM Björn Töpel <bjorn@xxxxxxxxxx> wrote:
>>
>> From: Björn Töpel <bjorn@xxxxxxxxxxxx>
>>
>> The RISC-V port copies the PGD table from init_mm/swapper_pg_dir to
>> all userland page tables, which means that if the PGD level table is
>> changed, other page tables has to be updated as well.
>>
>> Instead of having the PGD changes ripple out to all tables, the
>> synchronization can be avoided by pre-allocating the PGD entries/pages
>> at boot, avoiding the synchronization all together.
>>
>> This is currently done for the bpf/modules, and vmalloc PGD regions.
>> Extend this scheme for the PGD regions touched by memory hotplugging.
>>
>> Prepare the RISC-V port for memory hotplug by pre-allocate
>> vmemmap/direct map entries at the PGD level. This will roughly waste
>> ~128 worth of 4K pages when memory hotplugging is enabled in the
>> kernel configuration.
>>
>> Signed-off-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
>> ---
>> arch/riscv/include/asm/kasan.h | 4 ++--
>> arch/riscv/mm/init.c | 7 +++++++
>> 2 files changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/kasan.h b/arch/riscv/include/asm/kasan.h
>> index 0b85e363e778..e6a0071bdb56 100644
>> --- a/arch/riscv/include/asm/kasan.h
>> +++ b/arch/riscv/include/asm/kasan.h
>> @@ -6,8 +6,6 @@
>>
>> #ifndef __ASSEMBLY__
>>
>> -#ifdef CONFIG_KASAN
>> -
>> /*
>> * The following comment was copied from arm64:
>> * KASAN_SHADOW_START: beginning of the kernel virtual addresses.
>> @@ -34,6 +32,8 @@
>> */
>> #define KASAN_SHADOW_START ((KASAN_SHADOW_END - KASAN_SHADOW_SIZE) & PGDIR_MASK)
>> #define KASAN_SHADOW_END MODULES_LOWEST_VADDR
>> +
>> +#ifdef CONFIG_KASAN
>> #define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
>>
>> void kasan_init(void);
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 2574f6a3b0e7..5b8cdfafb52a 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -27,6 +27,7 @@
>>
>> #include <asm/fixmap.h>
>> #include <asm/io.h>
>> +#include <asm/kasan.h>
>> #include <asm/numa.h>
>> #include <asm/pgtable.h>
>> #include <asm/sections.h>
>> @@ -1488,10 +1489,16 @@ static void __init preallocate_pgd_pages_range(unsigned long start, unsigned lon
>> panic("Failed to pre-allocate %s pages for %s area\n", lvl, area);
>> }
>>
>> +#define PAGE_END KASAN_SHADOW_START
>> +
>> void __init pgtable_cache_init(void)
>> {
>> preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc");
>> if (IS_ENABLED(CONFIG_MODULES))
>> preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules");
>> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
>> + preallocate_pgd_pages_range(VMEMMAP_START, VMEMMAP_END, "vmemmap");
>> + preallocate_pgd_pages_range(PAGE_OFFSET, PAGE_END, "direct map");
>> + }
>> }
>> #endif
>> --
>> 2.40.1
>>
>
> As you asked, with
> https://lore.kernel.org/linux-riscv/20240514133614.87813-1-alexghiti@xxxxxxxxxxxx/T/#u,
> you will be able to remove the usage of KASAN_SHADOW_START.
Very nice -- consistency! I'll need to respin, so I'll clean this up for
the next version.
> But anyhow, you can add:
>
> Reviewed-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
Thank you!
Björn
