On 4/18/24 5:23 PM, benja...@sipsolutions.net wrote:
> diff --git a/arch/um/include/asm/mmu.h b/arch/um/include/asm/mmu.h
> index 37eb6e89e79a..bf8da736609c 100644
> --- a/arch/um/include/asm/mmu.h
> +++ b/arch/um/include/asm/mmu.h
> @@ -10,6 +10,10 @@
>
> typedef struct mm_context {
> struct mm_id id;
> +
> + /* Address range in need of a TLB sync */
> + long int sync_tlb_range_from;
> + long int sync_tlb_range_to;
Why not "unsigned long"?
> } mm_context_t;
>
> extern void __switch_mm(struct mm_id * mm_idp);
> diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
> index e1ece21dbe3f..5bb397b65efb 100644
> --- a/arch/um/include/asm/pgtable.h
> +++ b/arch/um/include/asm/pgtable.h
> @@ -244,6 +244,38 @@ static inline void set_pte(pte_t *pteptr, pte_t pteval)
>
> #define PFN_PTE_SHIFT PAGE_SHIFT
>
> +static inline void um_tlb_mark_sync(struct mm_struct *mm, unsigned long
> start,
> + unsigned long end)
> +{
> + if (!mm->context.sync_tlb_range_to) {
> + mm->context.sync_tlb_range_from = start;
> + mm->context.sync_tlb_range_to = end;
> + } else {
> + if (start < mm->context.sync_tlb_range_from)
> + mm->context.sync_tlb_range_from = start;
> + if (end > mm->context.sync_tlb_range_to)
> + mm->context.sync_tlb_range_to = end;
> + }
> +}
IIUC, in some cases, the range [sync_tlb_range_from, sync_tlb_range_to)
might become very large when merging non-adjacent ranges? Could that
be an issue?
> diff --git a/arch/um/include/asm/tlbflush.h b/arch/um/include/asm/tlbflush.h
> index d7cf82023b74..62816f6f1c91 100644
> --- a/arch/um/include/asm/tlbflush.h
> +++ b/arch/um/include/asm/tlbflush.h
> @@ -9,24 +9,50 @@
> #include <linux/mm.h>
>
> /*
> - * TLB flushing:
> + * In UML, we need to sync the TLB over by using mmap/munmap/mprotect
> syscalls
> + * from the process handling the MM (which can be the kernel itself).
> + *
> + * To track updates, we can hook into set_ptes and flush_tlb_*. With set_ptes
> + * we catch all PTE transitions where memory that was unusable becomes
> usable.
> + * While with flush_tlb_* we can track any memory that becomes unusable and
> + * even if a higher layer of the page table was modified.
> + *
> + * So, we simply track updates using both methods and mark the memory area to
> + * be synced later on. The only special case is that flush_tlb_kern_* needs
> to
> + * be executed immediately as there is no good synchronization point in that
> + * case. In contrast, in the set_ptes case we can wait for the next kernel
> + * segfault before we do the synchornization.
> *
> - * - flush_tlb() flushes the current mm struct TLBs
> * - flush_tlb_all() flushes all processes TLBs
> * - flush_tlb_mm(mm) flushes the specified mm context TLB's
> * - flush_tlb_page(vma, vmaddr) flushes one page
> - * - flush_tlb_kernel_vm() flushes the kernel vm area
> * - flush_tlb_range(vma, start, end) flushes a range of pages
> + * - flush_tlb_kernel_range(start, end) flushes a range of kernel pages
> */
>
> +extern int um_tlb_sync(struct mm_struct *mm);
> +
> extern void flush_tlb_all(void);
> extern void flush_tlb_mm(struct mm_struct *mm);
> -extern void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
> - unsigned long end);
> -extern void flush_tlb_page(struct vm_area_struct *vma, unsigned long
> address);
> -extern void flush_tlb_kernel_vm(void);
> -extern void flush_tlb_kernel_range(unsigned long start, unsigned long end);
> -extern void __flush_tlb_one(unsigned long addr);
> +
> +static void flush_tlb_page(struct vm_area_struct *vma, unsigned long address)
> +{
> + um_tlb_mark_sync(vma->vm_mm, address, address + PAGE_SIZE);
> +}
> +
> +static void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
> + unsigned long end)
> +{
> + um_tlb_mark_sync(vma->vm_mm, start, end);
> +}
> +
> +static void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> +{
> + um_tlb_mark_sync(&init_mm, start, end);
> +
> + /* Kernel needs to be synced immediately */
> + um_tlb_sync(&init_mm);
> +}
Nit: this is a header file, these functions should be defined as inline
functions.
> diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
> index c137ff6f84dd..232aa7601d5d 100644
> --- a/arch/um/kernel/tlb.c
> +++ b/arch/um/kernel/tlb.c
[...]
>
> -void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> -{
> - flush_tlb_kernel_range_common(start, end);
> -}
> -
> -void flush_tlb_kernel_vm(void)
> -{
> - flush_tlb_kernel_range_common(start_vm, end_vm);
> -}
The build breaks with this change, as there is still a call to
flush_tlb_kernel_vm() in ubd.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/um/drivers/ubd_kern.c?id=fb5d1d389c9e78d68f1f71f926d6251017579f5b#n774
Regards,
Tiwei
