Re: [Qemu-devel] MTTCG sync-up call today?

["Alex Bennée" <alex.bennee@linaro.org>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 12/01/2016 17:13, Alex Bennée wrote:
>> #4  0x00005555556e5b06 in tb_invalidate_phys_range (start=start@entry=0, end=end@entry=4096) at /home/alex/lsrc/qemu/qemu.git/translate-all.c:1303
>> #5  0x00005555556dbe42 in invalidate_and_set_dirty (mr=mr@entry=0x555556571800, addr=0, length=length@entry=4096) at /home/alex/lsrc/qemu/qemu.git/exec.c:2420
>> #6  0x00005555556e1890 in address_space_unmap (as=as@entry=0x555555ff7000 <address_space_memory>, buffer=<optimised out>, len=<optimised out>,
>>     is_write=is_write@entry=1, access_len=access_len@entry=4096) at /home/alex/lsrc/qemu/qemu.git/exec.c:2933
>> #7  0x00005555556e19bf in cpu_physical_memory_unmap (buffer=<optimised out>, len=<optimised out>, is_write=is_write@entry=1, access_len=access_len@entry=4096)
>>     at /home/alex/lsrc/qemu/qemu.git/exec.c:2962
>> #8  0x000055555578219c in virtqueue_unmap_sg (elem=elem@entry=0x7ffe782c7cf0, len=len@entry=4097, vq=0x555556e6f020)
>>     at /home/alex/lsrc/qemu/qemu.git/hw/virtio/virtio.c:257
>> #9  0x0000555555782ac0 in virtqueue_fill (vq=vq@entry=0x555556e6f020, elem=elem@entry=0x7ffe782c7cf0, len=4097, idx=idx@entry=0)
>>     at /home/alex/lsrc/qemu/qemu.git/hw/virtio/virtio.c:282
>> #10 0x0000555555782ccf in virtqueue_push (vq=0x555556e6f020, elem=elem@entry=0x7ffe782c7cf0, len=<optimised out>)
>>     at /home/alex/lsrc/qemu/qemu.git/hw/virtio/virtio.c:308
>> #11 0x000055555573451a in virtio_blk_complete_request (req=0x7ffe782c7ce0, status=<optimised out>) at /home/alex/lsrc/qemu/qemu.git/hw/block/virtio-blk.c:58
>> #12 0x0000555555734a13 in virtio_blk_req_complete (status=0 '\000', req=0x7ffe782c7ce0) at /home/alex/lsrc/qemu/qemu.git/hw/block/virtio-blk.c:64
>> #13 virtio_blk_rw_complete (opaque=<optimised out>, ret=0) at /home/alex/lsrc/qemu/qemu.git/hw/block/virtio-blk.c:122
>> ---Type <return> to continue, or q <return> to quit---
>> #14 0x0000555555a2d822 in bdrv_co_complete (acb=0x7ffe780189c0) at block/io.c:2122
>> #15 0x0000555555a87a7a in coroutine_trampoline (i0=<optimised out>, i1=<optimised out>) at util/coroutine-ucontext.c:80
>> #16 0x00007ffff0afc8b0 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
>> #17 0x00007fff8f5aa6e0 in ?? ()
>> #18 0x0000000000000000 in ?? ()
>>
>> I guess the tb_lock could just be grabbed but there is stuff in that
>> path that assumes current_cpu is valid so I thought the thing to do was
>> defer the operation until a "real" vCPU can deal with it.
>
> I need to look at the branch...  The latest version I have here does
> not require tb_lock taken in tb_invalidate_phys_range.

The tb_locks asserts where added in Fred's branch which makes sense as
we are going to mess with the translation block cache. Looking more
closely at tb_invalidate_phys_page_range I see it jumps through some
hoops when cpu == current_cpu == NULL.


>
> /*
>  * Invalidate all TBs which intersect with the target physical address range
>  * [start;end[. NOTE: start and end may refer to *different* physical pages.
>  * 'is_cpu_write_access' should be true if called from a real cpu write
>  * access: the virtual CPU will exit the current TB if code is modified inside
>  * this TB.
>  *
>  * Called with mmap_lock held for user-mode emulation
>  */
> void tb_invalidate_phys_range(tb_page_addr_t start, tb_page_addr_t end)
> {
>     while (start < end) {
>         tb_invalidate_phys_page_range(start, end, 0);
>         start &= TARGET_PAGE_MASK;
>         start += TARGET_PAGE_SIZE;
>     }
> }
>
> /*
>  * Invalidate all TBs which intersect with the target physical address range
>  * [start;end[. NOTE: start and end must refer to the *same* physical page.
>  * 'is_cpu_write_access' should be true if called from a real cpu write
>  * access: the virtual CPU will exit the current TB if code is modified inside
>  * this TB.
>  *
>  * Called with mmap_lock held for user-mode emulation
>  * If called from generated code, iothread mutex must not be held.
>  */
> void tb_invalidate_phys_page_range(tb_page_addr_t start, tb_page_addr_t end,
>                                    int is_cpu_write_access)
>
>
> Paolo


--
Alex Bennée