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Re: [Qemu-devel] [PATCH v2 10/23] RISC-V: Hold rcu_read_lock when access
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Qemu-devel] [PATCH v2 10/23] RISC-V: Hold rcu_read_lock when accessing memory |
Date: |
Sat, 10 Mar 2018 21:45:12 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 |
Hi Michael,
On 03/09/2018 05:12 AM, 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 <address@hidden>
> Cc: Bastian Koppelmann <address@hidden>
> CC: Stefan O'Rear <address@hidden>
> Signed-off-by: Michael Clark <address@hidden>
> Signed-off-by: Palmer Dabbelt <address@hidden>
> ---
> target/riscv/helper.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/target/riscv/helper.c b/target/riscv/helper.c
> index 02cbcea..228933c 100644
> --- a/target/riscv/helper.c
> +++ b/target/riscv/helper.c
> @@ -209,6 +209,7 @@ restart:
> as the PTE is no longer valid */
> MemoryRegion *mr;
> hwaddr l = sizeof(target_ulong), addr1;
> + rcu_read_lock();
> mr = address_space_translate(cs->as, pte_addr,
> &addr1, &l, false);
> if (memory_access_is_direct(mr, true)) {
> @@ -222,16 +223,19 @@ restart:
> target_ulong old_pte =
> atomic_cmpxchg(pte_pa, pte, updated_pte);
> if (old_pte != pte) {
> + rcu_read_unlock();
> goto restart;
> } else {
> pte = updated_pte;
> }
> #endif
> } else {
> + rcu_read_unlock();
> /* misconfigured PTE in ROM (AD bits are not preset) or
> * PTE is in IO space and can't be updated atomically */
> return TRANSLATE_FAIL;
> }
> + rcu_read_unlock();
Can you refactor to have a unique pair of lock/unlock?
This would be less bug-prone.
Thanks,
Phil.
> }
>
> /* for superpage mappings, make a fake leaf PTE for the TLB's
>
- [Qemu-devel] [PATCH v2 04/23] RISC-V: Use ROM base address and size from memmap, (continued)
- [Qemu-devel] [PATCH v2 04/23] RISC-V: Use ROM base address and size from memmap, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 05/23] RISC-V: Remove identity_translate from load_elf, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 03/23] RISC-V: Make virt board description match spike, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 06/23] RISC-V: Mark ROM read-only after copying in code, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 07/23] RISC-V: Remove unused class definitions, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 08/23] RISC-V: Make sure rom has space for fdt, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 09/23] RISC-V: Include intruction hex in disassembly, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 10/23] RISC-V: Hold rcu_read_lock when accessing memory, Michael Clark, 2018/03/08
- Re: [Qemu-devel] [PATCH v2 10/23] RISC-V: Hold rcu_read_lock when accessing memory,
Philippe Mathieu-Daudé <=
- [Qemu-devel] [PATCH v2 11/23] RISC-V: Improve page table walker spec compliance, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 12/23] RISC-V: Update E order and I extension order, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 14/23] RISC-V: Make virt header comment title consistent, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 13/23] RISC-V: Make some header guards more specific, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 16/23] RISC-V: Remove EM_RISCV ELF_MACHINE indirection, Michael Clark, 2018/03/08
- [Qemu-devel] [PATCH v2 15/23] RISC-V: Use memory_region_is_ram in pte update, Michael Clark, 2018/03/08