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* [PATCH] riscv: kasan: use local_tlb_flush_all() to avoid uninitialized __sbi_rfence
@ 2020-07-10  2:40 Vincent Chen
  2020-07-21  4:18 ` Palmer Dabbelt
  0 siblings, 1 reply; 3+ messages in thread
From: Vincent Chen @ 2020-07-10  2:40 UTC (permalink / raw)
  To: aryabinin, glider, dvyukov, paul.walmsley, palmer
  Cc: Vincent Chen, linux-riscv, nickhu

It fails to boot the v5.8-rc4 kernel with CONFIG_KASAN because kasan_init
and kasan_early_init use uninitialized __sbi_rfence as executing the
tlb_flush_all(). Actually, at this moment, only the CPU which is
responsible for the system initialization enables the MMU. Other CPUs are
parking at the .Lsecondary_start. Hence the tlb_flush_all() is able to be
replaced by local_tlb_flush_all() to avoid using uninitialized
__sbi_rfence.

Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
---
 arch/riscv/mm/kasan_init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
index 4a8b61806633..87b4ab3d3c77 100644
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -44,7 +44,7 @@ asmlinkage void __init kasan_early_init(void)
 				(__pa(((uintptr_t) kasan_early_shadow_pmd))),
 				__pgprot(_PAGE_TABLE)));
 
-	flush_tlb_all();
+	local_flush_tlb_all();
 }
 
 static void __init populate(void *start, void *end)
@@ -79,7 +79,7 @@ static void __init populate(void *start, void *end)
 			pfn_pgd(PFN_DOWN(__pa(&pmd[offset])),
 				__pgprot(_PAGE_TABLE)));
 
-	flush_tlb_all();
+	local_flush_tlb_all();
 	memset(start, 0, end - start);
 }
 
-- 
2.7.4


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^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] riscv: kasan: use local_tlb_flush_all() to avoid uninitialized __sbi_rfence
  2020-07-10  2:40 [PATCH] riscv: kasan: use local_tlb_flush_all() to avoid uninitialized __sbi_rfence Vincent Chen
@ 2020-07-21  4:18 ` Palmer Dabbelt
  2020-07-21  8:58   ` Vincent Chen
  0 siblings, 1 reply; 3+ messages in thread
From: Palmer Dabbelt @ 2020-07-21  4:18 UTC (permalink / raw)
  To: vincent.chen
  Cc: nickhu, vincent.chen, glider, Paul Walmsley, aryabinin,
	linux-riscv, dvyukov

On Thu, 09 Jul 2020 19:40:54 PDT (-0700), vincent.chen@sifive.com wrote:
> It fails to boot the v5.8-rc4 kernel with CONFIG_KASAN because kasan_init
> and kasan_early_init use uninitialized __sbi_rfence as executing the
> tlb_flush_all(). Actually, at this moment, only the CPU which is
> responsible for the system initialization enables the MMU. Other CPUs are
> parking at the .Lsecondary_start. Hence the tlb_flush_all() is able to be
> replaced by local_tlb_flush_all() to avoid using uninitialized
> __sbi_rfence.
>
> Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
> ---
>  arch/riscv/mm/kasan_init.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> index 4a8b61806633..87b4ab3d3c77 100644
> --- a/arch/riscv/mm/kasan_init.c
> +++ b/arch/riscv/mm/kasan_init.c
> @@ -44,7 +44,7 @@ asmlinkage void __init kasan_early_init(void)
>  				(__pa(((uintptr_t) kasan_early_shadow_pmd))),
>  				__pgprot(_PAGE_TABLE)));
>
> -	flush_tlb_all();
> +	local_flush_tlb_all();
>  }
>
>  static void __init populate(void *start, void *end)
> @@ -79,7 +79,7 @@ static void __init populate(void *start, void *end)
>  			pfn_pgd(PFN_DOWN(__pa(&pmd[offset])),
>  				__pgprot(_PAGE_TABLE)));
>
> -	flush_tlb_all();
> +	local_flush_tlb_all();
>  	memset(start, 0, end - start);
>  }

Can we just move the sbi_init() call before the kasan_init() call?  I feel like
the SBI should be initialized directly after paging, as probing really doesn't
have any dependencies.

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^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] riscv: kasan: use local_tlb_flush_all() to avoid uninitialized __sbi_rfence
  2020-07-21  4:18 ` Palmer Dabbelt
@ 2020-07-21  8:58   ` Vincent Chen
  0 siblings, 0 replies; 3+ messages in thread
From: Vincent Chen @ 2020-07-21  8:58 UTC (permalink / raw)
  To: Palmer Dabbelt
  Cc: nickhu, Alexander Potapenko, Paul Walmsley, aryabinin,
	linux-riscv, Dmitry Vyukov

On Tue, Jul 21, 2020 at 12:18 PM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Thu, 09 Jul 2020 19:40:54 PDT (-0700), vincent.chen@sifive.com wrote:
> > It fails to boot the v5.8-rc4 kernel with CONFIG_KASAN because kasan_init
> > and kasan_early_init use uninitialized __sbi_rfence as executing the
> > tlb_flush_all(). Actually, at this moment, only the CPU which is
> > responsible for the system initialization enables the MMU. Other CPUs are
> > parking at the .Lsecondary_start. Hence the tlb_flush_all() is able to be
> > replaced by local_tlb_flush_all() to avoid using uninitialized
> > __sbi_rfence.
> >
> > Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
> > ---
> >  arch/riscv/mm/kasan_init.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> > index 4a8b61806633..87b4ab3d3c77 100644
> > --- a/arch/riscv/mm/kasan_init.c
> > +++ b/arch/riscv/mm/kasan_init.c
> > @@ -44,7 +44,7 @@ asmlinkage void __init kasan_early_init(void)
> >                               (__pa(((uintptr_t) kasan_early_shadow_pmd))),
> >                               __pgprot(_PAGE_TABLE)));
> >
> > -     flush_tlb_all();
> > +     local_flush_tlb_all();
> >  }
> >
> >  static void __init populate(void *start, void *end)
> > @@ -79,7 +79,7 @@ static void __init populate(void *start, void *end)
> >                       pfn_pgd(PFN_DOWN(__pa(&pmd[offset])),
> >                               __pgprot(_PAGE_TABLE)));
> >
> > -     flush_tlb_all();
> > +     local_flush_tlb_all();
> >       memset(start, 0, end - start);
> >  }
>
> Can we just move the sbi_init() call before the kasan_init() call?  I feel like
> the SBI should be initialized directly after paging, as probing really doesn't
> have any dependencies.

The kasan_early_init() which is called before page_init() also uses
__sbi_rfence. Hence we need to move sbi_init() before the
kasan_early_init() not just before the kasan_init. I have tried to use
this solution to resolve this bug, and it could work on QEMU actually.
However, I think the solution replacing flush_tlb_all() with
local_flush_tlb_all() not only can resolve this problem but also can
lightly improve performance by reducing one SBI call. Therefore, the
patch uses local_flush_tlb_all() to solve this bug.

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^ permalink raw reply	[flat|nested] 3+ messages in thread

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2020-07-10  2:40 [PATCH] riscv: kasan: use local_tlb_flush_all() to avoid uninitialized __sbi_rfence Vincent Chen
2020-07-21  4:18 ` Palmer Dabbelt
2020-07-21  8:58   ` Vincent Chen

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