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

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-04-02 06:04, David Gibson wrote:
> From: Ben 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.
> 
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  kvm-all.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> I've sent this a number of times now, the last couple without comment.
> It fixes a real bug, please apply.
> 
> diff --git a/kvm-all.c b/kvm-all.c
> index ba2cee1..7e44429 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -354,6 +354,7 @@ static int kvm_get_dirty_pages_log_range(MemoryRegionSection *section,
>      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...)
> @@ -365,10 +366,11 @@ 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);
>          }
>      }

Ack for this, but - as proposed earlier - please add an
assert(TARGET_PAGE_SIZE <= getpagesize()) + comment to kvm_init().

Also, what's about coalesced MMIO? I see that the ring definition
depends on [TARGET_]PAGE_SIZE. What page size does the power kernel use
for it, and does it make a relevant difference for space?

Jan


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