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Re: [Qemu-devel] [PATCH] exec: Fix MAP_RAM for cached access
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] exec: Fix MAP_RAM for cached access |
Date: |
Wed, 13 Jun 2018 11:56:56 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 |
On 12/06/2018 21:05, Eric Auger wrote:
> When an IOMMUMemoryRegion is in front of a virtio device,
> address_space_cache_init does not set cache->ptr as the memory
> region is not RAM. However when the device performs an access,
> we end up in glue() which performs the translation and then uses
> MAP_RAM. This latter uses the unset ptr and returns a wrong value
> which leads to a SIGSEV in address_space_lduw_internal_cached_slow,
> for instance. Let's test whether the cache->ptr is set, and in
> the negative use the old macro definition. This fixes the
> use cases featuring vIOMMU (Intel and ARM SMMU) which lead to
> a SIGSEV.
>
> Fixes: 48564041a73a (exec: reintroduce MemoryRegion caching)
> Signed-off-by: Eric Auger <address@hidden>
>
> ---
>
> I am not sure whether it doesn't break any targeted optimization
> but at least it removes the SIGSEV.
Actually cache->ptr is always NULL here, since this is the slow path
(there is even an assertion in address_space_translate_cached); so
MAP_RAM can be even simpler and, apart from the bugfix, I think we
should remove all of IS_DIRECT, MAP_RAM and INVALIDATE as a follow-up.
They were needed in the original implementation of MemoryRegionCache,
which only worked with RAM regions but not anymore now that the RAM case
is open-coded in include/exec/memory_ldst_cached.inc.h.
Thanks,
Paolo
> Signed-off-by: Eric Auger <address@hidden>
> ---
> exec.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/exec.c b/exec.c
> index f6645ed..46fbd25 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3800,7 +3800,9 @@ address_space_write_cached_slow(MemoryRegionCache
> *cache, hwaddr addr,
> #define SUFFIX _cached_slow
> #define TRANSLATE(...) address_space_translate_cached(cache,
> __VA_ARGS__)
> #define IS_DIRECT(mr, is_write) memory_access_is_direct(mr, is_write)
> -#define MAP_RAM(mr, ofs) (cache->ptr + (ofs - cache->xlat))
> +#define MAP_RAM(mr, ofs) (cache->ptr ? \
> + (cache->ptr + (ofs - cache->xlat)) : \
> + qemu_map_ram_ptr((mr)->ram_block, ofs))
> #define INVALIDATE(mr, ofs, len) invalidate_and_set_dirty(mr, ofs, len)
> #define RCU_READ_LOCK() ((void)0)
> #define RCU_READ_UNLOCK() ((void)0)
>