From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 11D3BC4332F for ; Mon, 7 Nov 2022 17:25:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:Subject:Message-ID:Date:From: In-Reply-To:References:MIME-Version:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=SdOwoC1x112tFkWOKg4RzLkR9vduJsO8EM0ombDi49M=; b=TyfcZJrMixJEpb oGEd4mzuaB+9QGg8UlH5wW9umFvga9GrUKMc3OZ2ZrJ8NaJDh86Ye1h+yacOaPpVBJYEC8wc9+N8y hIjcF3Hh7t3+DxQWuXV84eYjhozyVsoPbG/CuOnidJVVJMIxIV9sr891hYNXXz/VouQ4MOxHAj3OI a0moAPO2W0nUEldzWTJcAAMn5i5DJ6jWmTHZZKh7NnEmpV82nq1Vc45gl5JEZ6kavDQ6FaTW/5IV1 PFqHxQIrC7VWMT1dklvQnUE+RIDDBGSM1YFhHDpL+qPv6RBIDSYrtC7msACC/SywExj0B7BW3UwyU 0ELbK+4E6L76WHZ9P53w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1os5s4-00Gezg-39; Mon, 07 Nov 2022 17:25:16 +0000 Received: from mail-ed1-x531.google.com ([2a00:1450:4864:20::531]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1os5rz-00Geuy-Er for linux-riscv@lists.infradead.org; Mon, 07 Nov 2022 17:25:13 +0000 Received: by mail-ed1-x531.google.com with SMTP id i21so18677640edj.10 for ; Mon, 07 Nov 2022 09:25:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20210112.gappssmtp.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=HMksJP+cg89DwngzLf3MGalvoSB3xfzUltruCjJaWFI=; b=nMZVZpF/rkW83ru3cSaCKTYrEqC7AepjXTsH4a1bDHllvsKQz89sPTtufK9PYd43QG 62LsdxqooPFiBmE8qy2hA2Z7TXvNLJPHMiE7TEGlxqtXIRwnRHcBAWM0PKZcZDoI9/+C v+fT90QdLp4OYHhUSyVgIi2MbTc6B4q525PlNNUD7EYvnVcsX+lJvS3ZM1pCH7c+rX4n PZeFexWqVqcXC95MeyH+8N/SNoePwbiUTyLTQ36idScNhfLr/mfWJty/ATAwE9t/9+Ub tz46bDpMTaKWh4cfSb8brNH7a9/jmxablW0QrlnsWs6YSQQEnZwylN4Fi+aS81utibf7 1Tew== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=HMksJP+cg89DwngzLf3MGalvoSB3xfzUltruCjJaWFI=; b=lLY8c8AjBM4ZtPfx19tERgPg5gAV0QWCH8GP16sdrPTEavYU0dW3IlmW7vXOQUQAcM IdyJizG8VRIrQ/29EpsNwq/mTTs1lUjJyGl5XNcyf8hA5FYb93ICC/cdctshs6KbNZs5 XJ4DXA1W319h9otyg+rDKbtkLtGM8jI1FvEcrz2d9czoRP8cTSyu4sxBk00Ae982dimB f4XrQG9jNQsA+FybUkytLbXRKRC3ylwrOavQSe9z7ihxj8QkJDtLcJMbWCT565Jn4b/7 BcARfqFEpBY+bDEb+YvuNrPy6KFndBJQMDyRgqZBABPgfi4HDOWyf1srcd7LiiMwO7L9 37nA== X-Gm-Message-State: ACrzQf2jSFrEfbqDuP4YhFehxDEOY34iC5+8OBTbBAIQOjskHgmdYdet EZtgkI/qAVhar30bSzwAH2z2FsE3nreDXMEIBJWsTg== X-Google-Smtp-Source: AMsMyM4RTHYiHYFnESK063Xo9ZQ8xYjNoqL2GfxS/Lvgwa6bvb7MHjFRyZEO92XGOo+P313DYDzK5RZ6+3V5BnnPoRA= X-Received: by 2002:aa7:d797:0:b0:462:1e07:1dd7 with SMTP id s23-20020aa7d797000000b004621e071dd7mr813331edq.293.1667841902929; Mon, 07 Nov 2022 09:25:02 -0800 (PST) MIME-Version: 1.0 References: <20221031213225.912258-1-geomatsi@gmail.com> In-Reply-To: From: Andrew Bresticker Date: Mon, 7 Nov 2022 12:24:51 -0500 Message-ID: Subject: Re: [RFC PATCH v1] riscv: support for hardware breakpoints/watchpoints To: Anup Patel Cc: Anup Patel , Sergey Matyukevich , linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, Atish Patra , Albert Ou , Palmer Dabbelt , Paul Walmsley , Sergey Matyukevich X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221107_092511_546484_3A2A39F7 X-CRM114-Status: GOOD ( 49.06 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Mon, Nov 7, 2022 at 11:06 AM Anup Patel wrote: > > On Mon, Nov 7, 2022 at 8:21 PM Andrew Bresticker wrote: > > > > On Sat, Nov 5, 2022 at 5:10 AM Anup Patel wrote: > > > > > > On Sat, Nov 5, 2022 at 3:07 AM Sergey Matyukevich wrote: > > > > > > > > Hi Andrew, > > > > > > > > > > RISC-V Debug specification includes Sdtrig ISA extension. This extension > > > > > > describes Trigger Module. Triggers can cause a breakpoint exception, > > > > > > entry into Debug Mode, or a trace action without having to execute a > > > > > > special instruction. For native debugging triggers can be used to > > > > > > implement hardware breakpoints and watchpoints. > > > > > > > > ... [snip] > > > > > > > > > > Despite missing userspace debug, initial implementation can be tested > > > > > > on QEMU using kernel breakpoints, e.g. see samples/hw_breakpoint and > > > > > > register_wide_hw_breakpoint. Hardware breakpoints work on upstream QEMU. > > > > > > > > > > We should also be able to enable the use of HW breakpoints (and > > > > > watchpoints, modulo the issue mentioned below) in kdb, right? > > > > > > > > Interesting. So far I didn't think about using hw breakpoints in kgdb. > > > > I took a quick look at riscv and arm64 kgdb code. It looks like there > > > > is nothing wrong in adding arch-specific implementation of the function > > > > 'kgdb_arch_set_breakpoint' that will use hw breakpoints if possible. > > > > Besides it looks like in this case it makes sense to handle KGDB earlier > > > > than hw breakpoints in do_trap_break. > > > > > > > > > > However this is not the case for watchpoints since there is no way to > > > > > > figure out which watchpoint is triggered. IIUC there are two possible > > > > > > options for doing this: using 'hit' bit in tdata1 or reading faulting > > > > > > virtual address from STVAL. QEMU implements neither of them. Current > > > > > > implementation opts for STVAL. So the following experimental QEMU patch > > > > > > is required to make watchpoints work: > > > > > > > > > > > > : diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c > > > > > > : index 278d163803..8858be7411 100644 > > > > > > : --- a/target/riscv/cpu_helper.c > > > > > > : +++ b/target/riscv/cpu_helper.c > > > > > > : @@ -1639,6 +1639,10 @@ void riscv_cpu_do_interrupt(CPUState *cs) > > > > > > : case RISCV_EXCP_VIRT_INSTRUCTION_FAULT: > > > > > > : tval = env->bins; > > > > > > : break; > > > > > > : + case RISCV_EXCP_BREAKPOINT: > > > > > > : + tval = env->badaddr; > > > > > > : + env->badaddr = 0x0; > > > > > > : + break; > > > > > > : default: > > > > > > : break; > > > > > > : } > > > > > > : diff --git a/target/riscv/debug.c b/target/riscv/debug.c > > > > > > : index 26ea764407..b4d1d566ab 100644 > > > > > > : --- a/target/riscv/debug.c > > > > > > : +++ b/target/riscv/debug.c > > > > > > : @@ -560,6 +560,7 @@ void riscv_cpu_debug_excp_handler(CPUState *cs) > > > > > > : > > > > > > : if (cs->watchpoint_hit) { > > > > > > : if (cs->watchpoint_hit->flags & BP_CPU) { > > > > > > : + env->badaddr = cs->watchpoint_hit->hitaddr; > > > > > > : cs->watchpoint_hit = NULL; > > > > > > : do_trigger_action(env, DBG_ACTION_BP); > > > > > > : } > > > > > > > > ... [snip] > > > > > > > > > > +int arch_install_hw_breakpoint(struct perf_event *bp) > > > > > > +{ > > > > > > + struct arch_hw_breakpoint *info = counter_arch_bp(bp); > > > > > > + struct sbi_dbtr_data_msg *xmit; > > > > > > + struct sbi_dbtr_id_msg *recv; > > > > > > + struct perf_event **slot; > > > > > > + struct sbiret ret; > > > > > > + int err = 0; > > > > > > + > > > > > > + xmit = kzalloc(SBI_MSG_SZ_ALIGN(sizeof(*xmit)), GFP_ATOMIC); > > > > > > + if (!xmit) { > > > > > > + err = -ENOMEM; > > > > > > + goto out; > > > > > > + } > > > > > > + > > > > > > + recv = kzalloc(SBI_MSG_SZ_ALIGN(sizeof(*recv)), GFP_ATOMIC); > > > > > > + if (!recv) { > > > > > > + err = -ENOMEM; > > > > > > + goto out; > > > > > > + } > > > > > > > > > > Do these really need to be dynamically allocated? > > > > > > > > According to SBI extension proposal, base address of this memory chunk > > > > must be 16-bytes aligned. To simplify things, buffer with 'power of two > > > > bytes' size (and >= 16 bytes) is allocated. In this case alignment of > > > > the kmalloc buffer is guaranteed to be at least this size. IIUC more > > > > efforts are needed to guarantee such alignment for a buffer on stack. > > > > You should be able to declare the struct with __aligned(16) to get the > > desired alignment on the stack. > > > > > Stack is not appropriate for this. Please use a per-CPU global > > > data for this purpose which should be 16 byte aligned as well. > > > > Is the desire to not use the stack purely a defensive measure, i.e. to > > defend against a buggy or malicious firmware/hypervisor? That's fine, > > I'm just curious if there's rationale beyond that (though I'd argue > > we're already implicitly trusting whatever software is sitting below > > us). > > The kernel stack is fixed size so it is best to avoid large structures > or arrays on kernel stack. Of course, though I'm not sure I'd consider 32 bytes "large" :) -Andrew > > Regards, > Anup > > > > > -Andrew > > > > > > > > You may also allocate a per-CPU 4K page at boot-time where > > > CPU X will use it's own 4K page for xmit (upper half) and > > > recv (lower half). > > > > > > Regards, > > > Anup > > > > > > > > > > > > > + > > > > > > + xmit->tdata1 = info->trig_data1.value; > > > > > > + xmit->tdata2 = info->trig_data2; > > > > > > + xmit->tdata3 = info->trig_data3; > > > > > > + > > > > > > + ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_TRIGGER_INSTALL, > > > > > > + 1, __pa(xmit) >> 4, __pa(recv) >> 4, > > > > > > + 0, 0, 0); > > > > > > + if (ret.error) { > > > > > > + pr_warn("%s: failed to install trigger\n", __func__); > > > > > > + err = -EIO; > > > > > > + goto out; > > > > > > + } > > > > > > + > > > > > > + if (recv->idx >= dbtr_total_num) { > > > > > > + pr_warn("%s: invalid trigger index %lu\n", __func__, recv->idx); > > > > > > + err = -EINVAL; > > > > > > + goto out; > > > > > > + } > > > > > > + > > > > > > + slot = this_cpu_ptr(&bp_per_reg[recv->idx]); > > > > > > + if (*slot) { > > > > > > + pr_warn("%s: slot %lu is in use\n", __func__, recv->idx); > > > > > > + err = -EBUSY; > > > > > > + goto out; > > > > > > + } > > > > > > + > > > > > > + *slot = bp; > > > > > > + > > > > > > +out: > > > > > > + kfree(xmit); > > > > > > + kfree(recv); > > > > > > + > > > > > > + return err; > > > > > > +} > > > > > > > > ... [snip] > > > > > > > > > > +static int __init arch_hw_breakpoint_init(void) > > > > > > +{ > > > > > > + union riscv_dbtr_tdata1 tdata1; > > > > > > + struct sbiret ret; > > > > > > + > > > > > > + if (sbi_probe_extension(SBI_EXT_DBTR) <= 0) { > > > > > > + pr_info("%s: SBI_EXT_DBTR is not supported\n", __func__); > > > > > > + return 0; > > > > > > + } > > > > > > + > > > > > > + ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_NUM_TRIGGERS, > > > > > > + 0, 0, 0, 0, 0, 0); > > > > > > + if (ret.error) { > > > > > > + pr_warn("%s: failed to detect triggers\n", __func__); > > > > > > + return 0; > > > > > > + } > > > > > > + > > > > > > + pr_info("%s: total number of triggers: %lu\n", __func__, ret.value); > > > > > > + > > > > > > + tdata1.value = 0; > > > > > > + tdata1.type = RISCV_DBTR_TRIG_MCONTROL6; > > > > > > + > > > > > > + ret = sbi_ecall(SBI_EXT_DBTR, SBI_EXT_DBTR_NUM_TRIGGERS, > > > > > > + tdata1.value, 0, 0, 0, 0, 0); > > > > > > + if (ret.error) { > > > > > > + pr_warn("%s: failed to detect triggers\n", __func__); > > > > > > + dbtr_total_num = 0; > > > > > > + return 0; > > > > > > + } > > > > > > > > > > nit: This is basically identical to hw_breakpoint_slots() -- just call > > > > > it here, or perhaps pull the DBTR_NUM_TRIGGERS ECALL into its own > > > > > function to reduce the duplication, e.g. 'dbtr_num_triggers(unsigned > > > > > long type)'? > > > > > > > > Good point. More similar requests will be added, e.g. for MCONTROL and > > > > possibly other trigger types. So I will add a separate > > > > 'dbtr_num_triggers' function. > > > > > > > > > > + > > > > > > + pr_info("%s: total number of type %d triggers: %lu\n", > > > > > > + __func__, tdata1.type, ret.value); > > > > > > + > > > > > > + dbtr_total_num = ret.value; > > > > > > + > > > > > > + return 0; > > > > > > +} > > > > > > > > Thanks! > > > > Sergey > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv