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Mon, 08 Jul 2019 01:26:34 -0700 (PDT) Received: from localhost ([134.17.27.127]) by smtp.gmail.com with ESMTPSA id b27sm1558817ljb.11.2019.07.08.01.26.33 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 08 Jul 2019 01:26:33 -0700 (PDT) Date: Mon, 08 Jul 2019 01:26:33 -0700 (PDT) X-Google-Original-Date: Mon, 08 Jul 2019 01:23:27 PDT (-0700) Subject: Re: [PATCH 16/17] riscv: clear the instruction cache and all registers when booting In-Reply-To: <78919862d11f6d56446f8fffd8a1a8c601ea5c32.camel@wdc.com> From: Palmer Dabbelt To: Atish Patra Message-ID: Mime-Version: 1.0 (MHng) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190708_012640_860543_14F4B5E6 X-CRM114-Status: GOOD ( 15.92 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Damien Le Moal , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Paul Walmsley , linux-riscv@lists.infradead.org, Christoph Hellwig Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org On Mon, 01 Jul 2019 14:26:18 PDT (-0700), Atish Patra wrote: > On Mon, 2019-06-24 at 07:43 +0200, Christoph Hellwig wrote: >> When we get booted we want a clear slate without any leaks from >> previous >> supervisors or the firmware. Flush the instruction cache and then >> clear >> all registers to known good values. This is really important for the >> upcoming nommu support that runs on M-mode, but can't really harm >> when >> running in S-mode either. > > That means it should be done for S-mode as well. Right ? > I see the reset code is enabled only for M-mode only. > >> Vaguely based on the concepts from opensbi. >> >> Signed-off-by: Christoph Hellwig >> --- >> arch/riscv/kernel/head.S | 85 >> ++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 85 insertions(+) >> >> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S >> index a4c170e41a34..74feb17737b4 100644 >> --- a/arch/riscv/kernel/head.S >> +++ b/arch/riscv/kernel/head.S >> @@ -11,6 +11,7 @@ >> #include >> #include >> #include >> +#include >> >> __INIT >> ENTRY(_start) >> @@ -19,6 +20,12 @@ ENTRY(_start) >> csrw CSR_XIP, zero >> >> #ifdef CONFIG_M_MODE >> + /* flush the instruction cache */ >> + fence.i >> + >> + /* Reset all registers except ra, a0, a1 */ >> + call reset_regs >> + >> /* >> * The hartid in a0 is expected later on, and we have no >> firmware >> * to hand it to us. >> @@ -168,6 +175,84 @@ relocate: >> j .Lsecondary_park >> END(_start) >> >> +#ifdef CONFIG_M_MODE >> +ENTRY(reset_regs) >> + li sp, 0 >> + li gp, 0 >> + li tp, 0 >> + li t0, 0 >> + li t1, 0 >> + li t2, 0 >> + li s0, 0 >> + li s1, 0 >> + li a2, 0 >> + li a3, 0 >> + li a4, 0 >> + li a5, 0 >> + li a6, 0 >> + li a7, 0 >> + li s2, 0 >> + li s3, 0 >> + li s4, 0 >> + li s5, 0 >> + li s6, 0 >> + li s7, 0 >> + li s8, 0 >> + li s9, 0 >> + li s10, 0 >> + li s11, 0 >> + li t3, 0 >> + li t4, 0 >> + li t5, 0 >> + li t6, 0 >> + csrw sscratch, 0 >> + >> +#ifdef CONFIG_FPU >> + csrr t0, misa >> + andi t0, t0, (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D) >> + bnez t0, .Lreset_regs_done >> + >> + li t1, SR_FS >> + csrs sstatus, t1 You need to check that the write stuck and branch around the FP instructions. Specifically, CONFIG_FPU means there may be an FPU, not there's definately an FPU. You should also turn the FPU back off after zeroing the state. >> + fmv.s.x f0, zero >> + fmv.s.x f1, zero >> + fmv.s.x f2, zero >> + fmv.s.x f3, zero >> + fmv.s.x f4, zero >> + fmv.s.x f5, zero >> + fmv.s.x f6, zero >> + fmv.s.x f7, zero >> + fmv.s.x f8, zero >> + fmv.s.x f9, zero >> + fmv.s.x f10, zero >> + fmv.s.x f11, zero >> + fmv.s.x f12, zero >> + fmv.s.x f13, zero >> + fmv.s.x f14, zero >> + fmv.s.x f15, zero >> + fmv.s.x f16, zero >> + fmv.s.x f17, zero >> + fmv.s.x f18, zero >> + fmv.s.x f19, zero >> + fmv.s.x f20, zero >> + fmv.s.x f21, zero >> + fmv.s.x f22, zero >> + fmv.s.x f23, zero >> + fmv.s.x f24, zero >> + fmv.s.x f25, zero >> + fmv.s.x f26, zero >> + fmv.s.x f27, zero >> + fmv.s.x f28, zero >> + fmv.s.x f29, zero >> + fmv.s.x f30, zero >> + fmv.s.x f31, zero >> + csrw fcsr, 0 >> +#endif /* CONFIG_FPU */ >> +.Lreset_regs_done: >> + ret >> +END(reset_regs) >> +#endif /* CONFIG_M_MODE */ >> + >> __PAGE_ALIGNED_BSS >> /* Empty zero page */ >> .balign PAGE_SIZE > > -- > Regards, > Atish _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv