Re: [Qemu-devel] [PATCH] exec.c: Fix subpage memory access to RAM MemoryRegion

[Avi Kivity <avi@redhat.com>]

On 11/28/2011 05:06 PM, Andreas Färber wrote:
> Commit 95c318f5e1f88d7e5bcc6deac17330fd4806a2d3 (Fix segfault in mmio subpage
> handling code.) prevented a segfault by making all subpage registrations
> over an existing memory page perform an unassigned access. Symptoms were
> writes not taking effect and reads returning zero.
>
> Very small page sizes are not currently supported either, so subpage memory
> areas cannot fully be avoided.
>
> Therefore revert the previous fix and defer recognition of IO_MEM_RAM to
> subpage_{read,write}len() and translate any access there.
>
> Signed-off-by: Andreas Färber <afaerber@suse.de>
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Gleb Natapov <gleb@redhat.com>
> Cc: Blue Swirl <blauwirbel@gmail.com>
> ---
>  exec.c |   33 +++++++++++++++++++++++++++++++--
>  1 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index 6b92198..fba5ba1 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3508,6 +3508,21 @@ static inline uint32_t subpage_readlen (subpage_t *mmio,
>  
>      addr += mmio->region_offset[idx];
>      idx = mmio->sub_io_index[idx];
> +    if (unlikely(idx == IO_MEM_RAM)) {

IMO, io_mem_init() should have something like

  cpu_register_io_memory_fixed(IO_MEM_SUBPAGE_RAM, subpage_ram_read,
subpage_ram_write, ...);

so you don't need those ugly switches; you just convert IO_MEM_RAM to
IO_MEM_SUBPAGE_RAM.  Maybe even register IO_MEM_RAM itself.  Note need
to handle dirty logging carefully.

-- 
error compiling committee.c: too many arguments to function