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Date:   Mon, 10 Feb 2020 09:59:31 -0800 (PST)
Subject:     Re: [PATCH] riscv: set pmp configuration if kernel is running in M-mode
In-Reply-To: <CAHCEeh+4a0O7tpp4dRXKudc6bmdJct=-H0SrPt=HbOs00T3-Hg@mail.gmail.com>
CC:     greentime@kernel.org, linux-riscv@lists.infradead.org,
        green.hu@gmail.com, linux-kernel@vger.kernel.org,
        Paul Walmsley <paul.walmsley@sifive.com>
From:   Palmer Dabbelt <palmerdabbelt@google.com>
To:     greentime.hu@sifive.com
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On Wed, 29 Jan 2020 18:38:43 PST (-0800), greentime.hu@sifive.com wrote:
> On Thu, Jan 30, 2020 at 3:23 AM Palmer Dabbelt <palmerdabbelt@google.com> wrote:
>>
>> On Thu, 09 Jan 2020 03:17:40 GMT (+0000), greentime.hu@sifive.com wrote:
>> > When the kernel is running in S-mode, the expectation is that the
>> > bootloader or SBI layer will configure the PMP to allow the kernel to
>> > access physical memory.  But, when the kernel is running in M-mode and is
>> > started with the ELF "loader", there's probably no bootloader or SBI layer
>> > involved to configure the PMP.  Thus, we need to configure the PMP
>> > ourselves to enable the kernel to access all regions.
>> >
>> > Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
>> > ---
>> >  arch/riscv/include/asm/csr.h | 12 ++++++++++++
>> >  arch/riscv/kernel/head.S     |  6 ++++++
>> >  2 files changed, 18 insertions(+)
>> >
>> > diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
>> > index 0a62d2d68455..0f25e6c4e45c 100644
>> > --- a/arch/riscv/include/asm/csr.h
>> > +++ b/arch/riscv/include/asm/csr.h
>> > @@ -72,6 +72,16 @@
>> >  #define EXC_LOAD_PAGE_FAULT  13
>> >  #define EXC_STORE_PAGE_FAULT 15
>> >
>> > +/* PMP configuration */
>> > +#define PMP_R                        0x01
>> > +#define PMP_W                        0x02
>> > +#define PMP_X                        0x04
>> > +#define PMP_A                        0x18
>> > +#define PMP_A_TOR            0x08
>> > +#define PMP_A_NA4            0x10
>> > +#define PMP_A_NAPOT          0x18
>> > +#define PMP_L                        0x80
>> > +
>> >  /* symbolic CSR names: */
>> >  #define CSR_CYCLE            0xc00
>> >  #define CSR_TIME             0xc01
>> > @@ -100,6 +110,8 @@
>> >  #define CSR_MCAUSE           0x342
>> >  #define CSR_MTVAL            0x343
>> >  #define CSR_MIP                      0x344
>> > +#define CSR_PMPCFG0          0x3a0
>> > +#define CSR_PMPADDR0         0x3b0
>> >  #define CSR_MHARTID          0xf14
>> >
>> >  #ifdef CONFIG_RISCV_M_MODE
>> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>> > index 5c8b24bf4e4e..f8f996916c5b 100644
>> > --- a/arch/riscv/kernel/head.S
>> > +++ b/arch/riscv/kernel/head.S
>> > @@ -60,6 +60,12 @@ _start_kernel:
>> >       /* Reset all registers except ra, a0, a1 */
>> >       call reset_regs
>> >
>> > +     /* Setup a PMP to permit access to all of memory. */
>> > +     li a0, -1
>> > +     csrw CSR_PMPADDR0, a0
>> > +     li a0, (PMP_A_NAPOT | PMP_R | PMP_W | PMP_X)
>> > +     csrw CSR_PMPCFG0, a0
>>
>> These should be guarded by some sort of #ifdef CONFIG_M_MODE, as they're not
>> part of S mode.
>
> Hi Palmer,
>
> This code segment is guarded by CONFIG_RISCV_M_MODE
>
> #ifdef CONFIG_RISCV_M_MODE
>         /* flush the instruction cache */
>         fence.i
>
>         /* Reset all registers except ra, a0, a1 */
>         call reset_regs
>
>         /* Setup a PMP to permit access to all of memory. */
>         li a0, -1
>         csrw CSR_PMPADDR0, a0
>         li a0, (PMP_A_NAPOT | PMP_R | PMP_W | PMP_X)
>         csrw CSR_PMPCFG0, a0
>
>         /*
>          * The hartid in a0 is expected later on, and we have no firmware
>          * to hand it to us.
>          */
>         csrr a0, CSR_MHARTID
> #endif /* CONFIG_RISCV_M_MODE */

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>

Whoops.  It's queued up for the RCs.