On 16/03/2018 20:41, Michael Clark wrote:
> From reading other code that accesses memory regions directly,
> it appears that the rcu_read_lock needs to be held. Note: the
> original code for accessing RAM directly was added because
> there is no other way to use atomic_cmpxchg on guest physical
> address space.
>
> Cc: Sagar Karandikar <sag...@eecs.berkeley.edu>
> Cc: Bastian Koppelmann <kbast...@mail.uni-paderborn.de>
> Signed-off-by: Michael Clark <m...@sifive.com>
> Signed-off-by: Palmer Dabbelt <pal...@sifive.com>
> ---
> target/riscv/helper.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
I think the bug here is that rcu_read_lock/unlock is missing in
cpu_memory_rw_debug. Are there any other callers you had in mind?
Paolo
> diff --git a/target/riscv/helper.c b/target/riscv/helper.c
> index 02cbcea..e71633a 100644
> --- a/target/riscv/helper.c
> +++ b/target/riscv/helper.c
> @@ -209,6 +209,9 @@ restart:
> as the PTE is no longer valid */
> MemoryRegion *mr;
> hwaddr l = sizeof(target_ulong), addr1;
> + enum { success, translate_fail, restart_walk} action =
> success;
> +
> + rcu_read_lock();
> mr = address_space_translate(cs->as, pte_addr,
> &addr1, &l, false);
> if (memory_access_is_direct(mr, true)) {
> @@ -222,7 +225,7 @@ restart:
> target_ulong old_pte =
> atomic_cmpxchg(pte_pa, pte, updated_pte);
> if (old_pte != pte) {
> - goto restart;
> + action = restart_walk;
> } else {
> pte = updated_pte;
> }
> @@ -230,7 +233,14 @@ restart:
> } else {
> /* misconfigured PTE in ROM (AD bits are not preset) or
> * PTE is in IO space and can't be updated atomically */
> - return TRANSLATE_FAIL;
> + action = translate_fail;
> + }
> + rcu_read_unlock();
> +
> + switch (action) {
> + case success: break;
> + case translate_fail: return TRANSLATE_FAIL;
> + case restart_walk: goto restart;
> }
> }
>
>
