[Qemu-devel] Re: [PATCH 2/3] Assume PPC64 host on PPC32 KVM

[Jan Kiszka <jan.kiszka@siemens.com>]

Alexander Graf wrote:
> When talking to the kernel about dirty maps, we need to find out which
> bits were actually set. This is done by set_bit and test_bit like
> functiontality which uses the "long" variable type.
> 
> Now, with PPC32 userspace and PPC64 kernel space (which is pretty common),
> we can't interpret the bits properly anymore, because we think long is
> 32 bits wide.
> 
> So for PPC dirty bitmap analysis, let's just assume we're always running
> on a PPC64 host. Currently there is no dirty bitmap implementation for
> PPC32 / PPCEMB anyways.
> 
> Unbreaks dirty logging on PPC.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  kvm-all.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/kvm-all.c b/kvm-all.c
> index 824bb4c..bfaa623 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -357,7 +357,13 @@ int kvm_physical_sync_dirty_bitmap(target_phys_addr_t start_addr,
>          for (phys_addr = mem->start_addr, addr = mem->phys_offset;
>               phys_addr < mem->start_addr + mem->memory_size;
>               phys_addr += TARGET_PAGE_SIZE, addr += TARGET_PAGE_SIZE) {
> +#ifdef HOST_PPC
> +             /* Big endian keeps us from having different long sizes in user and
> +              * kernel space, so assume we're always on ppc64. */
> +            uint64_t *bitmap = (uint64_t *)d.dirty_bitmap;
> +#else
>              unsigned long *bitmap = (unsigned long *)d.dirty_bitmap;
> +#endif
>              unsigned nr = (phys_addr - mem->start_addr) >> TARGET_PAGE_BITS;
>              unsigned word = nr / (sizeof(*bitmap) * 8);
>              unsigned bit = nr % (sizeof(*bitmap) * 8);

This rather screams for a generic fix. Current code assumes
sizeof(unsigned long) == 8. That should already break on 32-bit x86
hosts. So either do (sizeof(*bitmap) * sizeof(unsigned long)) or switch
to uint64_t - but for ALL hosts.

Jan

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