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Sun, 06 Jul 2025 20:54:03 -0700 (PDT) From: Anup Patel To: Atish Patra Cc: Palmer Dabbelt , Paul Walmsley , Alexandre Ghiti , Andrew Jones , Anup Patel , kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Anup Patel , Atish Patra , Heinrich Schuchardt Subject: [PATCH v2 2/2] RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization Date: Mon, 7 Jul 2025 09:23:44 +0530 Message-ID: <20250707035345.17494-3-apatel@ventanamicro.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250707035345.17494-1-apatel@ventanamicro.com> References: <20250707035345.17494-1-apatel@ventanamicro.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, the common AIA functions kvm_riscv_vcpu_aia_has_interrupts() and kvm_riscv_aia_wakeon_hgei() lookup HGEI line using an array of VCPU pointers before accessing HGEI[E|P] CSR which is slow and prone to race conditions because there is a separate per-hart lock for the VCPU pointer array and a separate per-VCPU rwlock for IMSIC VS-file (including HGEI line) used by the VCPU. Due to these race conditions, it is observed on QEMU RISC-V host that Guest VCPUs sleep in WFI and never wakeup even with interrupt pending in the IMSIC VS-file because VCPUs were waiting for HGEI wakeup on the wrong host CPU. The IMSIC virtualization already keeps track of the HGEI line and the associated IMSIC VS-file used by each VCPU so move the HGEI[E|P] CSR access to IMSIC virtualization so that costly HGEI line lookup can be avoided and likelihood of race-conditions when updating HGEI[E|P] CSR is also reduced. Reviewed-by: Atish Patra Tested-by: Atish Patra Tested-by: Heinrich Schuchardt Fixes: 3385339296d1 ("RISC-V: KVM: Use IMSIC guest files when available") Signed-off-by: Anup Patel Reviewed-by: Nutty Liu --- arch/riscv/include/asm/kvm_aia.h | 4 ++- arch/riscv/kvm/aia.c | 51 +++++--------------------------- arch/riscv/kvm/aia_imsic.c | 45 ++++++++++++++++++++++++++++ arch/riscv/kvm/vcpu.c | 2 -- 4 files changed, 55 insertions(+), 47 deletions(-) diff --git a/arch/riscv/include/asm/kvm_aia.h b/arch/riscv/include/asm/kvm_= aia.h index 0a0f12496f00..b04ecdd1a860 100644 --- a/arch/riscv/include/asm/kvm_aia.h +++ b/arch/riscv/include/asm/kvm_aia.h @@ -87,6 +87,9 @@ DECLARE_STATIC_KEY_FALSE(kvm_riscv_aia_available); =20 extern struct kvm_device_ops kvm_riscv_aia_device_ops; =20 +bool kvm_riscv_vcpu_aia_imsic_has_interrupt(struct kvm_vcpu *vcpu); +void kvm_riscv_vcpu_aia_imsic_load(struct kvm_vcpu *vcpu, int cpu); +void kvm_riscv_vcpu_aia_imsic_put(struct kvm_vcpu *vcpu); void kvm_riscv_vcpu_aia_imsic_release(struct kvm_vcpu *vcpu); int kvm_riscv_vcpu_aia_imsic_update(struct kvm_vcpu *vcpu); =20 @@ -161,7 +164,6 @@ void kvm_riscv_aia_destroy_vm(struct kvm *kvm); int kvm_riscv_aia_alloc_hgei(int cpu, struct kvm_vcpu *owner, void __iomem **hgei_va, phys_addr_t *hgei_pa); void kvm_riscv_aia_free_hgei(int cpu, int hgei); -void kvm_riscv_aia_wakeon_hgei(struct kvm_vcpu *owner, bool enable); =20 void kvm_riscv_aia_enable(void); void kvm_riscv_aia_disable(void); diff --git a/arch/riscv/kvm/aia.c b/arch/riscv/kvm/aia.c index 19afd1f23537..dad318185660 100644 --- a/arch/riscv/kvm/aia.c +++ b/arch/riscv/kvm/aia.c @@ -30,28 +30,6 @@ unsigned int kvm_riscv_aia_nr_hgei; unsigned int kvm_riscv_aia_max_ids; DEFINE_STATIC_KEY_FALSE(kvm_riscv_aia_available); =20 -static int aia_find_hgei(struct kvm_vcpu *owner) -{ - int i, hgei; - unsigned long flags; - struct aia_hgei_control *hgctrl =3D get_cpu_ptr(&aia_hgei); - - raw_spin_lock_irqsave(&hgctrl->lock, flags); - - hgei =3D -1; - for (i =3D 1; i <=3D kvm_riscv_aia_nr_hgei; i++) { - if (hgctrl->owners[i] =3D=3D owner) { - hgei =3D i; - break; - } - } - - raw_spin_unlock_irqrestore(&hgctrl->lock, flags); - - put_cpu_ptr(&aia_hgei); - return hgei; -} - static inline unsigned long aia_hvictl_value(bool ext_irq_pending) { unsigned long hvictl; @@ -95,7 +73,6 @@ void kvm_riscv_vcpu_aia_sync_interrupts(struct kvm_vcpu *= vcpu) =20 bool kvm_riscv_vcpu_aia_has_interrupts(struct kvm_vcpu *vcpu, u64 mask) { - int hgei; unsigned long seip; =20 if (!kvm_riscv_aia_available()) @@ -114,11 +91,7 @@ bool kvm_riscv_vcpu_aia_has_interrupts(struct kvm_vcpu = *vcpu, u64 mask) if (!kvm_riscv_aia_initialized(vcpu->kvm) || !seip) return false; =20 - hgei =3D aia_find_hgei(vcpu); - if (hgei > 0) - return !!(ncsr_read(CSR_HGEIP) & BIT(hgei)); - - return false; + return kvm_riscv_vcpu_aia_imsic_has_interrupt(vcpu); } =20 void kvm_riscv_vcpu_aia_update_hvip(struct kvm_vcpu *vcpu) @@ -164,6 +137,9 @@ void kvm_riscv_vcpu_aia_load(struct kvm_vcpu *vcpu, int= cpu) csr_write(CSR_HVIPRIO2H, csr->hviprio2h); #endif } + + if (kvm_riscv_aia_initialized(vcpu->kvm)) + kvm_riscv_vcpu_aia_imsic_load(vcpu, cpu); } =20 void kvm_riscv_vcpu_aia_put(struct kvm_vcpu *vcpu) @@ -174,6 +150,9 @@ void kvm_riscv_vcpu_aia_put(struct kvm_vcpu *vcpu) if (!kvm_riscv_aia_available()) return; =20 + if (kvm_riscv_aia_initialized(vcpu->kvm)) + kvm_riscv_vcpu_aia_imsic_put(vcpu); + if (kvm_riscv_nacl_available()) { nsh =3D nacl_shmem(); csr->vsiselect =3D nacl_csr_read(nsh, CSR_VSISELECT); @@ -472,22 +451,6 @@ void kvm_riscv_aia_free_hgei(int cpu, int hgei) raw_spin_unlock_irqrestore(&hgctrl->lock, flags); } =20 -void kvm_riscv_aia_wakeon_hgei(struct kvm_vcpu *owner, bool enable) -{ - int hgei; - - if (!kvm_riscv_aia_available()) - return; - - hgei =3D aia_find_hgei(owner); - if (hgei > 0) { - if (enable) - csr_set(CSR_HGEIE, BIT(hgei)); - else - csr_clear(CSR_HGEIE, BIT(hgei)); - } -} - static irqreturn_t hgei_interrupt(int irq, void *dev_id) { int i; diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c index ea1a36836d9c..fda0346f0ea1 100644 --- a/arch/riscv/kvm/aia_imsic.c +++ b/arch/riscv/kvm/aia_imsic.c @@ -677,6 +677,48 @@ static void imsic_swfile_update(struct kvm_vcpu *vcpu, imsic_swfile_extirq_update(vcpu); } =20 +bool kvm_riscv_vcpu_aia_imsic_has_interrupt(struct kvm_vcpu *vcpu) +{ + struct imsic *imsic =3D vcpu->arch.aia_context.imsic_state; + unsigned long flags; + bool ret =3D false; + + /* + * The IMSIC SW-file directly injects interrupt via hvip so + * only check for interrupt when IMSIC VS-file is being used. + */ + + read_lock_irqsave(&imsic->vsfile_lock, flags); + if (imsic->vsfile_cpu > -1) + ret =3D !!(csr_read(CSR_HGEIP) & BIT(imsic->vsfile_hgei)); + read_unlock_irqrestore(&imsic->vsfile_lock, flags); + + return ret; +} + +void kvm_riscv_vcpu_aia_imsic_load(struct kvm_vcpu *vcpu, int cpu) +{ + /* + * No need to explicitly clear HGEIE CSR bits because the + * hgei interrupt handler (aka hgei_interrupt()) will always + * clear it for us. + */ +} + +void kvm_riscv_vcpu_aia_imsic_put(struct kvm_vcpu *vcpu) +{ + struct imsic *imsic =3D vcpu->arch.aia_context.imsic_state; + unsigned long flags; + + if (!kvm_vcpu_is_blocking(vcpu)) + return; + + read_lock_irqsave(&imsic->vsfile_lock, flags); + if (imsic->vsfile_cpu > -1) + csr_set(CSR_HGEIE, BIT(imsic->vsfile_hgei)); + read_unlock_irqrestore(&imsic->vsfile_lock, flags); +} + void kvm_riscv_vcpu_aia_imsic_release(struct kvm_vcpu *vcpu) { unsigned long flags; @@ -781,6 +823,9 @@ int kvm_riscv_vcpu_aia_imsic_update(struct kvm_vcpu *vc= pu) * producers to the new IMSIC VS-file. */ =20 + /* Ensure HGEIE CSR bit is zero before using the new IMSIC VS-file */ + csr_clear(CSR_HGEIE, BIT(new_vsfile_hgei)); + /* Zero-out new IMSIC VS-file */ imsic_vsfile_local_clear(new_vsfile_hgei, imsic->nr_hw_eix); =20 diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c index fe028b4274df..b26bf35a0a19 100644 --- a/arch/riscv/kvm/vcpu.c +++ b/arch/riscv/kvm/vcpu.c @@ -211,12 +211,10 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu) =20 void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) { - kvm_riscv_aia_wakeon_hgei(vcpu, true); } =20 void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) { - kvm_riscv_aia_wakeon_hgei(vcpu, false); } =20 int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu) --=20 2.43.0