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Date: Thu, 29 Jul 2010 18:16:40 -0300
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20100729211640.GA10181@amt.cnet>
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Subject: [Qemu-devel] Re: [PATCH 1/2] Fix segfault in mmio subpage handling
	code.
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To: Gleb Natapov <gleb@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org

On Thu, Jul 29, 2010 at 01:41:45PM +0300, Gleb Natapov wrote:
> Use this one instead.
> 
> On Wed, Jul 28, 2010 at 06:13:22PM +0300, Gleb Natapov wrote:
> > It is possible that subpage mmio is registered over existing memory
> > page. When this happens "memory" will have real memory address and not
> > index into io_mem array so next access to the page will generate
> > segfault. It is uncommon to have some part of a page to be accessed as
> > memory and some as mmio, but qemu shouldn't crash even when guest does
> > stupid things. So lets just pretend that the rest of the page is
> > unassigned if guest configure part of the memory page as mmio.
> > 
> > Signed-off-by: Gleb Natapov <gleb@redhat.com>
> 
> diff --git a/exec.c b/exec.c
> index 5e9a5b7..53483bc 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3362,6 +3362,8 @@ static int subpage_register (subpage_t *mmio, uint32_t start, uint32_t end,
>      printf("%s: %p start %08x end %08x idx %08x eidx %08x mem %ld\n", __func__,
>             mmio, start, end, idx, eidx, memory);
>  #endif
> +    if ((memory & ~TARGET_PAGE_MASK) == IO_MEM_RAM)
> +        memory = IO_MEM_UNASSIGNED;
>      memory = (memory >> IO_MEM_SHIFT) & (IO_MEM_NB_ENTRIES - 1);
>      for (; idx <= eidx; idx++) {
>          mmio->sub_io_index[idx] = memory;

Looks good to me.