From 57f576e860d3a3582edb5064db9f0c95558ca5f4 Mon Sep 17 00:00:00 2001 From: Anup Patel Date: Mon, 7 Jul 2025 09:23:43 +0530 Subject: [PATCH 1/2] RISC-V: KVM: Disable vstimecmp before exiting to user-space If VS-timer expires when no VCPU running on a host CPU then WFI executed by such host CPU will be effective NOP resulting in no power savings. This is as-per RISC-V Privileged specificaiton which says: "WFI is also required to resume execution for locally enabled interrupts pending at any privilege level, regardless of the global interrupt enable at each privilege level." To address the above issue, vstimecmp CSR must be set to -1UL over here when VCPU is scheduled-out or exits to user space. Reviewed-by: Atish Patra Tested-by: Atish Patra Tested-by: Heinrich Schuchardt Fixes: 8f5cb44b1bae ("RISC-V: KVM: Support sstc extension") Fixes: cea8896bd936 ("RISC-V: KVM: Fix kvm_riscv_vcpu_timer_pending() for Sstc") Reported-by: Heinrich Schuchardt Closes: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2112578 Signed-off-by: Anup Patel Reviewed-by: Nutty Liu Link: https://lore.kernel.org/r/20250707035345.17494-2-apatel@ventanamicro.com Signed-off-by: Anup Patel --- arch/riscv/kvm/vcpu_timer.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/riscv/kvm/vcpu_timer.c b/arch/riscv/kvm/vcpu_timer.c index ff672fa71fcc..85a7262115e1 100644 --- a/arch/riscv/kvm/vcpu_timer.c +++ b/arch/riscv/kvm/vcpu_timer.c @@ -345,8 +345,24 @@ void kvm_riscv_vcpu_timer_save(struct kvm_vcpu *vcpu) /* * The vstimecmp CSRs are saved by kvm_riscv_vcpu_timer_sync() * upon every VM exit so no need to save here. + * + * If VS-timer expires when no VCPU running on a host CPU then + * WFI executed by such host CPU will be effective NOP resulting + * in no power savings. This is because as-per RISC-V Privileged + * specificaiton: "WFI is also required to resume execution for + * locally enabled interrupts pending at any privilege level, + * regardless of the global interrupt enable at each privilege + * level." + * + * To address the above issue, vstimecmp CSR must be set to -1UL + * over here when VCPU is scheduled-out or exits to user space. */ + csr_write(CSR_VSTIMECMP, -1UL); +#if defined(CONFIG_32BIT) + csr_write(CSR_VSTIMECMPH, -1UL); +#endif + /* timer should be enabled for the remaining operations */ if (unlikely(!t->init_done)) return; From 4cec89db80ba81fa4524c6449c0494b8ae08eeb0 Mon Sep 17 00:00:00 2001 From: Anup Patel Date: Mon, 7 Jul 2025 09:23:44 +0530 Subject: [PATCH 2/2] RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization 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 Link: https://lore.kernel.org/r/20250707035345.17494-3-apatel@ventanamicro.com Signed-off-by: Anup Patel --- arch/riscv/include/asm/kvm_aia.h | 4 ++- arch/riscv/include/asm/kvm_host.h | 3 ++ arch/riscv/kvm/aia.c | 51 +++++-------------------------- arch/riscv/kvm/aia_imsic.c | 45 +++++++++++++++++++++++++++ arch/riscv/kvm/vcpu.c | 10 ------ 5 files changed, 58 insertions(+), 55 deletions(-) diff --git a/arch/riscv/include/asm/kvm_aia.h b/arch/riscv/include/asm/kvm_aia.h index 3b643b9efc07..5acce285e56e 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); extern struct kvm_device_ops kvm_riscv_aia_device_ops; +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); @@ -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); void kvm_riscv_aia_enable(void); void kvm_riscv_aia_disable(void); diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h index 85cfebc32e4c..bcbf8b1ec115 100644 --- a/arch/riscv/include/asm/kvm_host.h +++ b/arch/riscv/include/asm/kvm_host.h @@ -306,6 +306,9 @@ static inline bool kvm_arch_pmi_in_guest(struct kvm_vcpu *vcpu) return IS_ENABLED(CONFIG_GUEST_PERF_EVENTS) && !!vcpu; } +static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {} +static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {} + #define KVM_RISCV_GSTAGE_TLB_MIN_ORDER 12 void kvm_riscv_local_hfence_gvma_vmid_gpa(unsigned long vmid, 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); -static int aia_find_hgei(struct kvm_vcpu *owner) -{ - int i, hgei; - unsigned long flags; - struct aia_hgei_control *hgctrl = get_cpu_ptr(&aia_hgei); - - raw_spin_lock_irqsave(&hgctrl->lock, flags); - - hgei = -1; - for (i = 1; i <= kvm_riscv_aia_nr_hgei; i++) { - if (hgctrl->owners[i] == owner) { - hgei = 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) bool kvm_riscv_vcpu_aia_has_interrupts(struct kvm_vcpu *vcpu, u64 mask) { - int hgei; unsigned long seip; 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; - hgei = 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); } 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); } 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; + if (kvm_riscv_aia_initialized(vcpu->kvm)) + kvm_riscv_vcpu_aia_imsic_put(vcpu); + if (kvm_riscv_nacl_available()) { nsh = nacl_shmem(); csr->vsiselect = 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); } -void kvm_riscv_aia_wakeon_hgei(struct kvm_vcpu *owner, bool enable) -{ - int hgei; - - if (!kvm_riscv_aia_available()) - return; - - hgei = 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 29ef9c2133a9..2ff865943ebb 100644 --- a/arch/riscv/kvm/aia_imsic.c +++ b/arch/riscv/kvm/aia_imsic.c @@ -676,6 +676,48 @@ static void imsic_swfile_update(struct kvm_vcpu *vcpu, imsic_swfile_extirq_update(vcpu); } +bool kvm_riscv_vcpu_aia_imsic_has_interrupt(struct kvm_vcpu *vcpu) +{ + struct imsic *imsic = vcpu->arch.aia_context.imsic_state; + unsigned long flags; + bool ret = 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 = !!(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 = 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 *vcpu) * producers to the new IMSIC VS-file. */ + /* 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); diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c index e0a01af426ff..0462863206ca 100644 --- a/arch/riscv/kvm/vcpu.c +++ b/arch/riscv/kvm/vcpu.c @@ -207,16 +207,6 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu) return kvm_riscv_vcpu_timer_pending(vcpu); } -void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) -{ - kvm_riscv_aia_wakeon_hgei(vcpu, true); -} - -void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) -{ - kvm_riscv_aia_wakeon_hgei(vcpu, false); -} - int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu) { return (kvm_riscv_vcpu_has_interrupts(vcpu, -1UL) &&