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Date:   Tue, 27 Sep 2022 08:18:38 +0800
From:   Jisheng Zhang <jszhang@kernel.org>
To:     Guo Ren <guoren@kernel.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Subject: Re: [PATCH 3/4] riscv: fix race when vmap stack overflow and remove
 shadow_stack
Message-ID: <YzJBXsiWrbmxM6Q2@xhacker>
References: <20220925175356.681-1-jszhang@kernel.org>
 <20220925175356.681-4-jszhang@kernel.org>
 <CAJF2gTRFXwu5QtA8GywGaSVRPA7zeexcDHRzcngcY1zD3MFjog@mail.gmail.com>
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> >  #ifdef CONFIG_VMAP_STACK
> > -static DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
> > -               overflow_stack)__aligned(16);
> > -/*
> > - * shadow stack, handled_ kernel_ stack_ overflow(in kernel/entry.S) is used
> > - * to get per-cpu overflow stack(get_overflow_stack).
> > - */
> > -long shadow_stack[SHADOW_OVERFLOW_STACK_SIZE/sizeof(long)];
> > -asmlinkage unsigned long get_overflow_stack(void)
> > -{
> > -       return (unsigned long)this_cpu_ptr(overflow_stack) +
> > -               OVERFLOW_STACK_SIZE;
> > -}
> > +unsigned long overflow_stack[NR_CPUS][OVERFLOW_STACK_SIZE/sizeof(long)] __aligned(16);

If NR_CPUS is large, there's a non-trival memory waste, I have a
solution for this case, will send a new version today.

Thanks