On Mon, Aug 5, 2024 at 8:21 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote:
>
> Pause remote CPUs so that the local CPU can follow the proper BBM
> sequence to safely update the vmemmap mapping `struct page` areas.
>
> While updating the vmemmap, it is guaranteed that neither the local
> CPU nor the remote ones will access the `struct page` area being
> updated, and therefore they will not trigger kernel PFs.
>
> Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/pgalloc.h | 55 ++++++++++++++++++++++++++++++++
> mm/hugetlb_vmemmap.c | 14 ++++++++
> 2 files changed, 69 insertions(+)
>
> diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
> index 8ff5f2a2579e..1af1aa34a351 100644
> --- a/arch/arm64/include/asm/pgalloc.h
> +++ b/arch/arm64/include/asm/pgalloc.h
> @@ -12,6 +12,7 @@
> #include <asm/processor.h>
> #include <asm/cacheflush.h>
> #include <asm/tlbflush.h>
> +#include <asm/cpu.h>
>
> #define __HAVE_ARCH_PGD_FREE
> #define __HAVE_ARCH_PUD_FREE
> @@ -137,4 +138,58 @@ pmd_populate(struct mm_struct *mm, pmd_t *pmdp, pgtable_t ptep)
> __pmd_populate(pmdp, page_to_phys(ptep), PMD_TYPE_TABLE | PMD_TABLE_PXN);
> }
>
> +#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
> +
> +#define vmemmap_update_lock vmemmap_update_lock
> +static inline void vmemmap_update_lock(void)
> +{
> + cpus_read_lock();
> +}
> +
> +#define vmemmap_update_unlock vmemmap_update_unlock
> +static inline void vmemmap_update_unlock(void)
> +{
> + cpus_read_unlock();
> +}
> +
> +#define vmemmap_update_pte vmemmap_update_pte
> +static inline void vmemmap_update_pte(unsigned long addr, pte_t *ptep, pte_t pte)
> +{
> + preempt_disable();
> + pause_remote_cpus();
> +
> + pte_clear(&init_mm, addr, ptep);
> + flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
> + set_pte_at(&init_mm, addr, ptep, pte);
> +
> + resume_remote_cpus();
> + preempt_enable();
> +}
Note that I kept this API from Nanyong for the sake of discussion.
What I actually plan to test in our production is:
#define vmemmap_update_pte_range_start vmemmap_update_pte_range_start
static inline void vmemmap_update_pte_range_start(pte_t *pte,
unsigned long start,
unsigned long end)
{
preempt_disable();
pause_remote_cpus();
for (; start != end; start += PAGE_SIZE, pte++)
pte_clear(&init_mm, start, pte);
flush_tlb_kernel_range(start, end);
}
#define vmemmap_update_pte_range_end vmemmap_update_pte_range_end
static inline void vmemmap_update_pte_range_end(void)
{
resume_remote_cpus();
preempt_enable();
}
> +#define vmemmap_update_pmd vmemmap_update_pmd
> +static inline void vmemmap_update_pmd(unsigned long addr, pmd_t *pmdp, pte_t *ptep)
> +{
> + preempt_disable();
> + pause_remote_cpus();
> +
> + pmd_clear(pmdp);
> + flush_tlb_kernel_range(addr, addr + PMD_SIZE);
> + pmd_populate_kernel(&init_mm, pmdp, ptep);
> +
> + resume_remote_cpus();
> + preempt_enable();
> +}
> +
> +#define vmemmap_flush_tlb_all vmemmap_flush_tlb_all
> +static inline void vmemmap_flush_tlb_all(void)
> +{
> +}
> +
> +#define vmemmap_flush_tlb_range vmemmap_flush_tlb_range
> +static inline void vmemmap_flush_tlb_range(unsigned long start, unsigned long end)
> +{
> +}
> +
> +#endif /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
> +
> #endif
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 2dd92e58f304..893c73493d9c 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -46,6 +46,18 @@ struct vmemmap_remap_walk {
> unsigned long flags;
> };
>
> +#ifndef vmemmap_update_lock
> +static void vmemmap_update_lock(void)
> +{
> +}
> +#endif
> +
> +#ifndef vmemmap_update_unlock
> +static void vmemmap_update_unlock(void)
> +{
> +}
> +#endif
> +
> #ifndef vmemmap_update_pmd
> static inline void vmemmap_update_pmd(unsigned long addr,
> pmd_t *pmdp, pte_t *ptep)
> @@ -194,10 +206,12 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
>
> VM_BUG_ON(!PAGE_ALIGNED(start | end));
>
> + vmemmap_update_lock();
> mmap_read_lock(&init_mm);
> ret = walk_page_range_novma(&init_mm, start, end, &vmemmap_remap_ops,
> NULL, walk);
> mmap_read_unlock(&init_mm);
> + vmemmap_update_unlock();
> if (ret)
> return ret;
>
> --
> 2.46.0.rc2.264.g509ed76dc8-goog
>
