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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8AB73C433EF for ; Sat, 23 Jul 2022 04:47:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236869AbiGWErY (ORCPT ); Sat, 23 Jul 2022 00:47:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229975AbiGWErW (ORCPT ); Sat, 23 Jul 2022 00:47:22 -0400 Received: from mail-wm1-x335.google.com (mail-wm1-x335.google.com [IPv6:2a00:1450:4864:20::335]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7306A30F72 for ; Fri, 22 Jul 2022 21:47:20 -0700 (PDT) Received: by mail-wm1-x335.google.com with SMTP id b6so3802980wmq.5 for ; Fri, 22 Jul 2022 21:47:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=brainfault-org.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ClkRR6M+900US0KQHHRgn2sKqC8Wt2qOmc26396rdLw=; b=sCzL+HDv0axLrw3jxXM06IvPYPBB/FqyaN5CzcyIs518O6+S5/Hq6HW0Vtm8IrrN9a JlEoRO3fzJcqMiA5rECLNcZUTyfzZnduc6XmJoxXEIJ4Fa/i/mBRTN4a226oLGfZOy1T ZrOZBGtNb7jDv4c4cLT3HU2K5LAR+2K5qxKy6mRUcO2lMTPYGngWJngUi1s/49AZATMi vHTWJRjvVmdXTABGUuRMNhvtBEEH/zpdBUjLdv/kWoG/AC6eD7wkYIXXobgqA2vPgvCH dCy+zmkL6e/pgjUzPS+fawOaB4WCErjeADN8Gx2KtQfWmuQ65cHlJvW6YycGCCVgB0Pd VwEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ClkRR6M+900US0KQHHRgn2sKqC8Wt2qOmc26396rdLw=; b=mEowwkV6PEZ3g8kg+5Nlts20SlxWPsI+4qHRUTTIPmgIofB7vZu7UC8EolUO/w4bOV ufLLyOVNllj6KPz3QPba1GAXDknGNYZPgaZBSVCZzBywBZ43n7UcfF8tbVTkke+jh765 FLeUbKFv0Z6TkBFzWkHj0pbjxKXSbx6n2TXiXqKT+ufDHzbC0sUtXata4LyiiqaFqfLC ylLdBdauKcGTlmC+6JtAxr9a8rxeK781lgfSjJHmzd2Bff5Tmiu47bTT+iykBML/HhB9 ETRfb4wS1oSUb5bTspGmg/bfEEI0B1cUoxqMmq9cUb8APA1a9kw3YWWYw6t+o8/OpC17 FmLw== X-Gm-Message-State: AJIora+6jT+nwsAOSR/I2sMb6Y0F0swXb5uWobt/kL11T9T5NhzROc++ da8PgF7R+gcOHyLBO+WVu0S4zdb2zrmiChIQpkpNpw== X-Google-Smtp-Source: AGRyM1vdTDHnXx6/iSL72TAIkM2o5HPzQQpmceFlCysZbho0p1KKEyC2jfWh5dOmd2LLx/uobVYvmK1JdDJJLKgFhWQ= X-Received: by 2002:a05:600c:3caa:b0:394:8fb8:716 with SMTP id bg42-20020a05600c3caa00b003948fb80716mr14237697wmb.105.1658551638574; Fri, 22 Jul 2022 21:47:18 -0700 (PDT) MIME-Version: 1.0 References: <20220722165047.519994-1-atishp@rivosinc.com> In-Reply-To: <20220722165047.519994-1-atishp@rivosinc.com> From: Anup Patel Date: Sat, 23 Jul 2022 10:17:06 +0530 Message-ID: Subject: Re: [PATCH v7 0/4] Add Sstc extension support To: Atish Patra Cc: linux-kernel@vger.kernel.org, Albert Ou , Atish Patra , Daniel Lezcano , Guo Ren , Heiko Stuebner , kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , Paolo Bonzini , Paul Walmsley , Rob Herring , Thomas Gleixner , Tsukasa OI , Wei Fu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Palmer, On Fri, Jul 22, 2022 at 10:20 PM Atish Patra wrote: > > This series implements Sstc extension support which was ratified recently. > Before the Sstc extension, an SBI call is necessary to generate timer > interrupts as only M-mode have access to the timecompare registers. Thus, > there is significant latency to generate timer interrupts at kernel. > For virtualized enviornments, its even worse as the KVM handles the SBI call > and uses a software timer to emulate the timecomapre register. > > Sstc extension solves both these problems by defining a stimecmp/vstimecmp > at supervisor (host/guest) level. It allows kernel to program a timer and > recieve interrupt without supervisor execution enviornment (M-mode/HS mode) > intervention. > > KVM directly updates the vstimecmp as well if the guest kernel invokes the SBI > call instead of updating stimecmp directly. This is required because KVM will > enable sstc extension if the hardware supports it unless the VMM explicitly > disables it for that guest. The hardware is expected to compare the > vstimecmp at every cycle if sstc is enabled and any stale value in vstimecmp > will lead to spurious timer interrupts. This also helps maintaining the > backward compatibility with older kernels. > > Similary, the M-mode firmware(OpenSBI) uses stimecmp for older kernel > without sstc support as STIP bit in mip is read only for hardware with sstc. > > The PATCH 1 & 2 enables the basic infrastructure around Sstc extension while > PATCH 3 lets kernel use the Sstc extension if it is available in hardware. > PATCH 4 implements the Sstc extension in KVM. > > This series has been tested on Qemu(RV32 & RV64) with additional patches in > Qemu[2]. This series can also be found at [3]. > > Changes from v6->v7: > 1. Fixed a compilation error reported by 0-day bot. > > Changes from v5->v6: > 1. Moved SSTC extension enum below SVPBMT. > > Changes from v4->v5: > 1. Added RB tag. > 2. Changed the pr-format. > 3. Rebased on 5.19-rc7 and kvm-queue. > 4. Moved the henvcfg modification from hardware enable to vcpu_load. > > Changes from v3->v4: > 1. Rebased on 5.18-rc6 > 2. Unified vstimemp & next_cycles. > 3. Addressed comments in PATCH 3 & 4. > > Changes from v2->v3: > 1. Dropped unrelated KVM fixes from this series. > 2. Rebased on 5.18-rc3. > > Changes from v1->v2: > 1. Separate the static key from kvm usage > 2. Makde the sstc specific static key local to the driver/clocksource > 3. Moved the vstimecmp update code to the vcpu_timer > 4. Used function pointers instead of static key to invoke vstimecmp vs > hrtimer at the run time. This will help in future for migration of vms > from/to sstc enabled hardware to non-sstc enabled hardware. > 5. Unified the vstimer & timer to 1 timer as only one of them will be used > at runtime. > > [1] https://drive.google.com/file/d/1m84Re2yK8m_vbW7TspvevCDR82MOBaSX/view > [2] https://github.com/atishp04/qemu/tree/sstc_v6 > [3] https://github.com/atishp04/linux/tree/sstc_v7 > > Atish Patra (4): > RISC-V: Add SSTC extension CSR details > RISC-V: Enable sstc extension parsing from DT > RISC-V: Prefer sstc extension if available > RISC-V: KVM: Support sstc extension The PATCH4 is dependent on the KVM patches in queue for 5.20. I suggest you take PATCH1, PATCH2 and PATCH3. I will send PATCH4 in second batch/PR for 5.20 assuming you will send the first three patches in your first PR for 5.20 Does this sound okay to you ? Regards, Anup > > arch/riscv/include/asm/csr.h | 5 + > arch/riscv/include/asm/hwcap.h | 1 + > arch/riscv/include/asm/kvm_vcpu_timer.h | 7 ++ > arch/riscv/include/uapi/asm/kvm.h | 1 + > arch/riscv/kernel/cpu.c | 1 + > arch/riscv/kernel/cpufeature.c | 1 + > arch/riscv/kvm/vcpu.c | 8 +- > arch/riscv/kvm/vcpu_timer.c | 144 +++++++++++++++++++++++- > drivers/clocksource/timer-riscv.c | 25 +++- > 9 files changed, 185 insertions(+), 8 deletions(-) > > -- > 2.25.1 >