Re: [Qemu-devel] [PATCH 6/6] kvm: Fix dirty tracking with large kernel page size

[Blue Swirl <blauwirbel@gmail.com>]

On Fri, Feb 24, 2012 at 00:23, David Gibson <david@gibson.dropbear.id.au> wrote:
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>
> If the kernel page size is larger than TARGET_PAGE_SIZE, which
> happens for example on ppc64 with kernels compiled for 64K pages,
> the dirty tracking doesn't work.

I think a better solution would be to push this to memory API and
underlying exec.c dirty tracking so that they use the same page size
as kernel (only in this KVM case, in general dirty tracking should
match TARGET_PAGE_SIZE granularity).

> Cc: Avi Kivity <avi@redhat.com>
> Cc: Marcelo Tossatti <mtossatti@redhat.com>
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  kvm-all.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kvm-all.c b/kvm-all.c
> index 5e188bf..3f8cfd9 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -348,10 +348,11 @@ static int kvm_set_migration_log(int enable)
>  static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
>                                          unsigned long *bitmap)
>  {
> -    unsigned int i, j;
> +  unsigned int i, j;
>     unsigned long page_number, c;
>     target_phys_addr_t addr, addr1;
>     unsigned int len = ((section->size / TARGET_PAGE_SIZE) + HOST_LONG_BITS - 1) / HOST_LONG_BITS;
> +    unsigned long hpratio = getpagesize() / TARGET_PAGE_SIZE;
>
>     /*
>      * bitmap-traveling is faster than memory-traveling (for addr...)
> @@ -363,10 +364,10 @@ static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
>             do {
>                 j = ffsl(c) - 1;
>                 c &= ~(1ul << j);
> -                page_number = i * HOST_LONG_BITS + j;
> +                page_number = (i * HOST_LONG_BITS + j) * hpratio;
>                 addr1 = page_number * TARGET_PAGE_SIZE;
>                 addr = section->offset_within_region + addr1;
> -                memory_region_set_dirty(section->mr, addr, TARGET_PAGE_SIZE);
> +                memory_region_set_dirty(section->mr, addr, TARGET_PAGE_SIZE * hpratio);
>             } while (c != 0);
>         }
>     }
> --
> 1.7.9
>
>