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Wed, 03 Jan 2024 21:07:00 -0800 (PST) X-Google-Smtp-Source: AGHT+IHtRRfPoD2AmDU6qtptVCBW0QbNzJYM+ha8MKoofBpriej1vuzGKEnPUsoFlW2M8rLqW0B82A== X-Received: by 2002:a17:903:2448:b0:1d4:418e:d83b with SMTP id l8-20020a170903244800b001d4418ed83bmr67071pls.111.1704344819948; Wed, 03 Jan 2024 21:06:59 -0800 (PST) Received: from LeoBras.redhat.com ([2804:431:c7ec:911:6911:ca60:846:eb46]) by smtp.gmail.com with ESMTPSA id e1-20020a170902ed8100b001d4ab4e2a7asm8332870plj.231.2024.01.03.21.06.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Jan 2024 21:06:59 -0800 (PST) From: Leonardo Bras To: guoren@kernel.org Cc: Leonardo Bras , paul.walmsley@sifive.com, palmer@dabbelt.com, panqinglin2020@iscas.ac.cn, bjorn@rivosinc.com, conor.dooley@microchip.com, peterz@infradead.org, anup@brainfault.org, keescook@chromium.org, wuwei2016@iscas.ac.cn, xiaoguang.xing@sophgo.com, chao.wei@sophgo.com, unicorn_wang@outlook.com, uwu@icenowy.me, jszhang@kernel.org, wefu@redhat.com, atishp@atishpatra.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, Guo Ren Subject: Re: [PATCH V12 07/14] riscv: qspinlock: Add virt_spin_lock() support for VM guest Date: Thu, 4 Jan 2024 02:06:46 -0300 Message-ID: X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231225125847.2778638-8-guoren@kernel.org> References: <20231225125847.2778638-1-guoren@kernel.org> <20231225125847.2778638-8-guoren@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit On Mon, Dec 25, 2023 at 07:58:40AM -0500, guoren@kernel.org wrote: > From: Guo Ren > > Add a static key controlling whether virt_spin_lock() should be > called or not. When running on bare metal set the new key to > false. > > The VM guests should fall back to a Test-and-Set spinlock, > because fair locks have horrible lock 'holder' preemption issues. > The virt_spin_lock_key would shortcut for the queued_spin_lock_- > slowpath() function that allow virt_spin_lock to hijack it. > > Signed-off-by: Guo Ren > Signed-off-by: Guo Ren > --- > .../admin-guide/kernel-parameters.txt | 4 +++ > arch/riscv/include/asm/spinlock.h | 22 ++++++++++++++++ > arch/riscv/kernel/setup.c | 26 +++++++++++++++++++ > 3 files changed, 52 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 2ac9f1511774..b7794c96d91e 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3997,6 +3997,10 @@ > no_uaccess_flush > [PPC] Don't flush the L1-D cache after accessing user data. > > + no_virt_spin [RISC-V] Disable virt_spin_lock in VM guest to use > + native_queued_spinlock when the nopvspin option is enabled. > + This would help vcpu=pcpu scenarios. > + > novmcoredd [KNL,KDUMP] > Disable device dump. Device dump allows drivers to > append dump data to vmcore so you can collect driver > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h > index d07643c07aae..7bbcf3d9fff0 100644 > --- a/arch/riscv/include/asm/spinlock.h > +++ b/arch/riscv/include/asm/spinlock.h > @@ -4,6 +4,28 @@ > #define __ASM_RISCV_SPINLOCK_H > > #ifdef CONFIG_QUEUED_SPINLOCKS > +/* > + * The KVM guests fall back to a Test-and-Set spinlock, because fair locks > + * have horrible lock 'holder' preemption issues. The virt_spin_lock_key > + * would shortcut for the queued_spin_lock_slowpath() function that allow > + * virt_spin_lock to hijack it. > + */ > +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); > + > +#define virt_spin_lock virt_spin_lock > +static inline bool virt_spin_lock(struct qspinlock *lock) > +{ > + if (!static_branch_likely(&virt_spin_lock_key)) > + return false; > + > + do { > + while (atomic_read(&lock->val) != 0) > + cpu_relax(); > + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0); > + > + return true; > +} > + > #define _Q_PENDING_LOOPS (1 << 9) > #endif > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > index d9072a59831c..0bafb9fd6ea3 100644 > --- a/arch/riscv/kernel/setup.c > +++ b/arch/riscv/kernel/setup.c > @@ -27,6 +27,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -266,6 +267,27 @@ early_param("qspinlock", queued_spinlock_setup); > DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key); > EXPORT_SYMBOL(combo_qspinlock_key); > > +#ifdef CONFIG_QUEUED_SPINLOCKS > +static bool no_virt_spin __ro_after_init; > +static int __init no_virt_spin_setup(char *p) > +{ > + no_virt_spin = true; > + > + return 0; > +} > +early_param("no_virt_spin", no_virt_spin_setup); > + > +DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); > + > +static void __init virt_spin_lock_init(void) > +{ > + if (no_virt_spin) > + static_branch_disable(&virt_spin_lock_key); > + else > + pr_info("Enable virt_spin_lock\n"); > +} > +#endif > + > static void __init riscv_spinlock_init(void) > { > if (!enable_qspinlock) { > @@ -274,6 +296,10 @@ static void __init riscv_spinlock_init(void) > } else { > pr_info("Queued spinlock: enabled\n"); > } > + > +#ifdef CONFIG_QUEUED_SPINLOCKS > + virt_spin_lock_init(); > +#endif > } > #endif > > -- > 2.40.1 > LGTM: Reviewed-by: Leonardo Bras