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From: Andrea Parri <parri.andrea@gmail.com>
To: Guo Ren <guoren@kernel.org>
Cc: Jisheng Zhang <jszhang@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: fix race when vmap stack overflow
Date: Fri, 21 Oct 2022 10:36:35 +0200	[thread overview]
Message-ID: <Y1JaE/ot91Z0KXuC@andrea> (raw)
In-Reply-To: <CAJF2gTRAEX_jQ_w5H05dyafZzHq+P5j05TJ=C+v+OL__GQam4A@mail.gmail.com>

> > > +     atomic_set_release(&spin_shadow_stack, 0);
> >
> > Have not really looked the details: should there be a matching acquire?
> 
> I use atomic_set_release here, because I need earlier memory
> operations finished to make sure the sp is ready then set the spin
> flag.
> 
> The following memory operations order is not important, because we
> just care about sp value.
> 
> Also, we use relax amoswap before, because sp has naturelly
> dependency. But giving them RCsc is okay here, because we don't care
> about performance here.

Thanks for the clarification.

I'm not really suggesting to add unneeded synchronization, even more
so in local/private constructs as in this case.  It just felt odd to
see the release without a pairing acquire, so I asked.  ;-)

Thanks,
  Andrea


> eg:
>  handle_kernel_stack_overflow:
> +1:     la sp, spin_shadow_stack
> +       amoswap.w.aqrl sp, sp, (sp)
> +       bnez sp, 1b
> +
> ....
> +     smp_store_release(&spin_shadow_stack, 0);
> +     smp_mb();

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WARNING: multiple messages have this Message-ID (diff)
From: Andrea Parri <parri.andrea@gmail.com>
To: Guo Ren <guoren@kernel.org>
Cc: Jisheng Zhang <jszhang@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: fix race when vmap stack overflow
Date: Fri, 21 Oct 2022 10:36:35 +0200	[thread overview]
Message-ID: <Y1JaE/ot91Z0KXuC@andrea> (raw)
In-Reply-To: <CAJF2gTRAEX_jQ_w5H05dyafZzHq+P5j05TJ=C+v+OL__GQam4A@mail.gmail.com>

> > > +     atomic_set_release(&spin_shadow_stack, 0);
> >
> > Have not really looked the details: should there be a matching acquire?
> 
> I use atomic_set_release here, because I need earlier memory
> operations finished to make sure the sp is ready then set the spin
> flag.
> 
> The following memory operations order is not important, because we
> just care about sp value.
> 
> Also, we use relax amoswap before, because sp has naturelly
> dependency. But giving them RCsc is okay here, because we don't care
> about performance here.

Thanks for the clarification.

I'm not really suggesting to add unneeded synchronization, even more
so in local/private constructs as in this case.  It just felt odd to
see the release without a pairing acquire, so I asked.  ;-)

Thanks,
  Andrea


> eg:
>  handle_kernel_stack_overflow:
> +1:     la sp, spin_shadow_stack
> +       amoswap.w.aqrl sp, sp, (sp)
> +       bnez sp, 1b
> +
> ....
> +     smp_store_release(&spin_shadow_stack, 0);
> +     smp_mb();

  reply	other threads:[~2022-10-21  8:36 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-19 15:47 [PATCH] riscv: fix race when vmap stack overflow Jisheng Zhang
2022-10-19 15:47 ` Jisheng Zhang
2022-10-20  1:02 ` Guo Ren
2022-10-20  1:02   ` Guo Ren
2022-10-20  2:16 ` Guo Ren
2022-10-20  2:16   ` Guo Ren
2022-10-20 14:38   ` Jisheng Zhang
2022-10-20 14:38     ` Jisheng Zhang
2022-10-21  0:35     ` Guo Ren
2022-10-21  0:35       ` Guo Ren
2022-10-20 23:26 ` Andrea Parri
2022-10-20 23:26   ` Andrea Parri
2022-10-21  1:11   ` Guo Ren
2022-10-21  1:11     ` Guo Ren
2022-10-21  8:36     ` Andrea Parri [this message]
2022-10-21  8:36       ` Andrea Parri
2022-10-21 12:08       ` Tong Tiangen
2022-10-21 12:08         ` Tong Tiangen
2022-10-21 13:22         ` Andrea Parri
2022-10-21 13:22           ` Andrea Parri
2022-10-21 13:46           ` Tong Tiangen
2022-10-21 13:46             ` Tong Tiangen
2022-10-21 14:41             ` Guo Ren
2022-10-21 14:41               ` Guo Ren
2022-10-21 15:17               ` Tong Tiangen
2022-10-21 15:17                 ` Tong Tiangen
2022-10-21 14:35       ` Guo Ren
2022-10-21 14:35         ` Guo Ren

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