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Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set |
Date: |
Mon, 18 Jul 2016 19:11:55 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
On 18/07/2016 19:07, Sergey Fedorov wrote:
> On 18/07/16 20:00, Paolo Bonzini wrote:
>>
>> On 18/07/2016 18:57, Sergey Fedorov wrote:
>>> On 18/07/16 19:53, Paolo Bonzini wrote:
>>>> On 18/07/2016 18:52, Sergey Fedorov wrote:
>>>>> So how are we going to use them?
>>>> Instead of atomic_read/atomic_set when marking invalid TBs.
>>> But shouldn't they be atomic to avoid reading torn writes?
>> A torn write would probably fail to match anyway, but even if it doesn't
>> it is indistinguishable from a race, isn't it?
>
> I'm afraid, torn write can happen to be a false match against a wrong
> TB. In case of a race with atomic access we either get the right TB or
> an invalid one which couldn't match any valid CPU state. Probably, we
> have to make sure (and document this) that TB invalidation process
> cannot make a partially invalidated TB which can match any meaningful
> CPU state.
x86 is atomic (because flags are 32-bit); those that have cs_base==0 are
safe against torn writes too. Only SPARC perhaps could use
"tb->cs_base|=1" instead in case 0xffffffff........ matches another TB.
Paolo
>>
>> By the way, tb_cmp should also use volatile_read.
>
> You are right, we must user the save type of access in tb_cmp().
>
> Thanks,
> Sergey
>
- [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Sergey Fedorov, 2016/07/18
- Re: [Qemu-devel] [PATCH] atomics: add volatile_read/volatile_set, Paolo Bonzini, 2016/07/18