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Re: [Qemu-devel] [PATCH v7 04/14] icount: exit cpu loop on expire
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v7 04/14] icount: exit cpu loop on expire |
Date: |
Wed, 25 Jan 2017 12:06:04 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 |
On 24/01/2017 08:17, Pavel Dovgalyuk wrote:
> This patch adds check to break cpu loop when icount expires without
> setting the TB_EXIT_ICOUNT_EXPIRED flag. It happens when there is no
> available translated blocks and all instructions were executed.
> In icount replay mode unnecessary tb_find will be called (which may
> cause an exception) and execution will be non-deterministic.
>
> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> ---
> cpu-exec.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/cpu-exec.c b/cpu-exec.c
> index 79a2167..e603da4 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -582,9 +582,6 @@ static inline void cpu_loop_exec_tb(CPUState *cpu,
> TranslationBlock *tb,
> cpu_exec_nocache(cpu, insns_left, *last_tb, false);
> align_clocks(sc, cpu);
> }
> - cpu->exception_index = EXCP_INTERRUPT;
> - *last_tb = NULL;
> - cpu_loop_exit(cpu);
> }
> break;
> #endif
> @@ -638,6 +635,18 @@ int cpu_exec(CPUState *cpu)
>
> for(;;) {
> cpu_handle_interrupt(cpu, &last_tb);
> + /* icount has expired, we need to break the execution loop.
> + This check is needed before tb_find to make execution
> + deterministic - tb_find may cause an exception
> + while translating the code from non-mapped page. */
> + if (use_icount && ((cpu->icount_extra == 0
> + && cpu->icount_decr.u16.low == 0)
> + || (int32_t)cpu->icount_decr.u32 < 0)) {
> + if (cpu->exception_index == -1) {
> + cpu->exception_index = EXCP_INTERRUPT;
> + }
> + cpu_loop_exit(cpu);
> + }
Can this can be placed in cpu_handle_interrupt itself? Also, can the
cpu->exception_index != -1 case happen?
We really should add assertions on cpu->exception_index, maybe after
cpu_handle_exception and cc->cpu_exec_interrupt returns true. Without
some idea of the invariants, I'm not competent enough to review this patch.
Paolo
> tb = tb_find(cpu, last_tb, tb_exit);
> cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc);
> /* Try to align the host and virtual clocks
>
- [Qemu-devel] [PATCH v7 01/14] icount: update instruction counter on apic patching, (continued)
- [Qemu-devel] [PATCH v7 01/14] icount: update instruction counter on apic patching, Pavel Dovgalyuk, 2017/01/24
- [Qemu-devel] [PATCH v7 02/14] replay: improve interrupt handling, Pavel Dovgalyuk, 2017/01/24
- [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Pavel Dovgalyuk, 2017/01/24
- Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Paolo Bonzini, 2017/01/25
- Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Pavel Dovgalyuk, 2017/01/25
- Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Paolo Bonzini, 2017/01/25
- Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Pavel Dovgalyuk, 2017/01/25
- Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Paolo Bonzini, 2017/01/25
- Re: [Qemu-devel] [PATCH v7 03/14] replay: exception replay fix, Pavel Dovgalyuk, 2017/01/25
[Qemu-devel] [PATCH v7 04/14] icount: exit cpu loop on expire, Pavel Dovgalyuk, 2017/01/24
- Re: [Qemu-devel] [PATCH v7 04/14] icount: exit cpu loop on expire,
Paolo Bonzini <=
[Qemu-devel] [PATCH v7 05/14] apic: save apic_delivered flag, Pavel Dovgalyuk, 2017/01/24
[Qemu-devel] [PATCH v7 06/14] replay: don't use rtc clock on loadvm phase, Pavel Dovgalyuk, 2017/01/24
[Qemu-devel] [PATCH v7 08/14] savevm: add public save_vmstate function, Pavel Dovgalyuk, 2017/01/24