On Mon, Feb 28, 2011 at 11:59:07AM +0000, Russell King wrote:
> It may be hacky but then the TLB shootdown interface is hacky too. We
> don't keep the vma around to re-use after tlb_end_vma() - if you think
> that then you misunderstand what's going on. The vma pointer is kept
> around as a cheap way of allowing tlb_finish_mmu() to distinguish
> between the unmap_region() mode and the shift_arg_pages() mode.
As I think I mentioned, the TLB shootdown interface either needs rewriting
from scratch as its currently a broken design, or it needs tlb_gather_mmu()
to take a proper mode argument, rather than this useless 'fullmm' argument
which only gives half the story.
The fact is that the interface has three modes, and distinguishing between
them requires a certain amount of black magic. Explicitly, the !fullmm
case has two modes, and it requires implementations to remember whether
tlb_start_vma() has been called before tlb_finish_mm() or not.
Maybe this will help you understand the ARM implementation - this doesn't
change the functionality, but may make things clearer.
diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index 82dfe5d..73fb813 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h
@@ -54,7 +54,7 @@
struct mmu_gather {
struct mm_struct *mm;
unsigned int fullmm;
- struct vm_area_struct *vma;
+ unsigned int byvma;
unsigned long range_start;
unsigned long range_end;
unsigned int nr;
@@ -68,23 +68,18 @@ DECLARE_PER_CPU(struct mmu_gather, mmu_gathers);
* code is used:
* 1. Unmapping a range of vmas. See zap_page_range(), unmap_region().
* tlb->fullmm = 0, and tlb_start_vma/tlb_end_vma will be called.
- * tlb->vma will be non-NULL.
+ * tlb->byvma will be true.
* 2. Unmapping all vmas. See exit_mmap().
* tlb->fullmm = 1, and tlb_start_vma/tlb_end_vma will be called.
- * tlb->vma will be non-NULL. Additionally, page tables will be freed.
+ * tlb->byvma will be true. Additionally, page tables will be freed.
* 3. Unmapping argument pages. See shift_arg_pages().
* tlb->fullmm = 0, but tlb_start_vma/tlb_end_vma will not be called.
- * tlb->vma will be NULL.
+ * tlb->byvma will be false.
*/
static inline void tlb_flush(struct mmu_gather *tlb)
{
- if (tlb->fullmm || !tlb->vma)
+ if (tlb->fullmm || !tlb->byvma)
flush_tlb_mm(tlb->mm);
- else if (tlb->range_end > 0) {
- flush_tlb_range(tlb->vma, tlb->range_start, tlb->range_end);
- tlb->range_start = TASK_SIZE;
- tlb->range_end = 0;
- }
}
static inline void tlb_add_flush(struct mmu_gather *tlb, unsigned long addr)
@@ -113,7 +108,7 @@ tlb_gather_mmu(struct mm_struct *mm, unsigned int full_mm_flush)
tlb->mm = mm;
tlb->fullmm = full_mm_flush;
- tlb->vma = NULL;
+ tlb->byvma = 0;
tlb->nr = 0;
return tlb;
@@ -149,7 +144,7 @@ tlb_start_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
{
if (!tlb->fullmm) {
flush_cache_range(vma, vma->vm_start, vma->vm_end);
- tlb->vma = vma;
+ tlb->byvma = 1;
tlb->range_start = TASK_SIZE;
tlb->range_end = 0;
}
@@ -158,8 +153,11 @@ tlb_start_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
static inline void
tlb_end_vma(struct mmu_gather *tlb, struct vm_area_struct *vma)
{
- if (!tlb->fullmm)
- tlb_flush(tlb);
+ if (!tlb->fullmm && tlb->range_end > 0) {
+ flush_tlb_range(vma, tlb->range_start, tlb->range_end);
+ tlb->range_start = TASK_SIZE;
+ tlb->range_end = 0;
+ }
}
static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
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