From 4ad3a0b87f2ec4714fdfa6bd5de57b4c30e15753 Mon Sep 17 00:00:00 2001 From: Oliver Upton Date: Thu, 19 Dec 2024 14:41:11 -0800 Subject: [PATCH] KVM: arm64: Don't hijack guest context MDSCR_EL1 Stealing MDSCR_EL1 in the guest's kvm_cpu_context for external debugging is rather gross. Just add a field for this instead and let the context switch code pick the correct one based on the debug owner. Tested-by: James Clark Signed-off-by: Oliver Upton Link: https://lore.kernel.org/r/20241219224116.3941496-15-oliver.upton@linux.dev Signed-off-by: Marc Zyngier --- arch/arm64/include/asm/kvm_host.h | 2 +- arch/arm64/kvm/debug.c | 75 +++++++++++----------- arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 39 +++++++---- 3 files changed, 64 insertions(+), 52 deletions(-) diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h index c630d59e7f4c..e7036096d9c2 100644 --- a/arch/arm64/include/asm/kvm_host.h +++ b/arch/arm64/include/asm/kvm_host.h @@ -751,6 +751,7 @@ struct kvm_vcpu_arch { */ struct kvm_guest_debug_arch vcpu_debug_state; struct kvm_guest_debug_arch external_debug_state; + u64 external_mdscr_el1; enum { VCPU_DEBUG_FREE, @@ -771,7 +772,6 @@ struct kvm_vcpu_arch { * are using guest debug. */ struct { - u32 mdscr_el1; bool pstate_ss; } guest_debug_preserved; diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c index cc9599a7df5f..db3d74e63bc3 100644 --- a/arch/arm64/kvm/debug.c +++ b/arch/arm64/kvm/debug.c @@ -31,19 +31,12 @@ */ static void save_guest_debug_regs(struct kvm_vcpu *vcpu) { - u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1); - - vcpu->arch.guest_debug_preserved.mdscr_el1 = val; vcpu->arch.guest_debug_preserved.pstate_ss = (*vcpu_cpsr(vcpu) & DBG_SPSR_SS); } static void restore_guest_debug_regs(struct kvm_vcpu *vcpu) { - u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1; - - vcpu_write_sys_reg(vcpu, val, MDSCR_EL1); - if (vcpu->arch.guest_debug_preserved.pstate_ss) *vcpu_cpsr(vcpu) |= DBG_SPSR_SS; else @@ -115,8 +108,6 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu) void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) { - unsigned long mdscr; - /* Check if we need to use the debug registers. */ if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) { /* Save guest debug state */ @@ -154,36 +145,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) *vcpu_cpsr(vcpu) |= DBG_SPSR_SS; else *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS; - - mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); - mdscr |= DBG_MDSCR_SS; - vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); - } else { - mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); - mdscr &= ~DBG_MDSCR_SS; - vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); - } - - /* - * Enable breakpoints and watchpoints if userspace wants them. - */ - if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) { - mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); - mdscr |= DBG_MDSCR_MDE; - vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); - - /* - * The OS Lock blocks debug exceptions in all ELs when it is - * enabled. If the guest has enabled the OS Lock, constrain its - * effects to the guest. Emulate the behavior by clearing - * MDSCR_EL1.MDE. In so doing, we ensure that host debug - * exceptions are unaffected by guest configuration of the OS - * Lock. - */ - } else if (kvm_vcpu_os_lock_enabled(vcpu)) { - mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); - mdscr &= ~DBG_MDSCR_MDE; - vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); } } } @@ -227,6 +188,41 @@ void kvm_init_host_debug_data(void) host_data_set_flag(HAS_TRBE); } +/* + * Configures the 'external' MDSCR_EL1 value for the guest, i.e. when the host + * has taken over MDSCR_EL1. + * + * - Userspace is single-stepping the guest, and MDSCR_EL1.SS is forced to 1. + * + * - Userspace is using the breakpoint/watchpoint registers to debug the + * guest, and MDSCR_EL1.MDE is forced to 1. + * + * - The guest has enabled the OS Lock, and KVM is forcing MDSCR_EL1.MDE to 0, + * masking all debug exceptions affected by the OS Lock. + */ +static void setup_external_mdscr(struct kvm_vcpu *vcpu) +{ + /* + * Use the guest's MDSCR_EL1 as a starting point, since there are + * several other features controlled by MDSCR_EL1 that are not relevant + * to the host. + * + * Clear the bits that KVM may use which also satisfies emulation of + * the OS Lock as MDSCR_EL1.MDE is cleared. + */ + u64 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1) & ~(MDSCR_EL1_SS | + MDSCR_EL1_MDE | + MDSCR_EL1_KDE); + + if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) + mdscr |= MDSCR_EL1_SS; + + if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) + mdscr |= MDSCR_EL1_MDE | MDSCR_EL1_KDE; + + vcpu->arch.external_mdscr_el1 = mdscr; +} + void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu) { u64 mdscr; @@ -249,6 +245,7 @@ void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu) */ if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) { vcpu->arch.debug_owner = VCPU_DEBUG_HOST_OWNED; + setup_external_mdscr(vcpu); } else { mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h index a998b2f6abcb..76ff095c6b6e 100644 --- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h +++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h @@ -18,9 +18,34 @@ static inline bool ctxt_has_s1poe(struct kvm_cpu_context *ctxt); +static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt) +{ + struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu; + + if (!vcpu) + vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt); + + return vcpu; +} + +static inline bool ctxt_is_guest(struct kvm_cpu_context *ctxt) +{ + return host_data_ptr(host_ctxt) != ctxt; +} + +static inline u64 *ctxt_mdscr_el1(struct kvm_cpu_context *ctxt) +{ + struct kvm_vcpu *vcpu = ctxt_to_vcpu(ctxt); + + if (ctxt_is_guest(ctxt) && kvm_host_owns_debug_regs(vcpu)) + return &vcpu->arch.external_mdscr_el1; + + return &ctxt_sys_reg(ctxt, MDSCR_EL1); +} + static inline void __sysreg_save_common_state(struct kvm_cpu_context *ctxt) { - ctxt_sys_reg(ctxt, MDSCR_EL1) = read_sysreg(mdscr_el1); + *ctxt_mdscr_el1(ctxt) = read_sysreg(mdscr_el1); // POR_EL0 can affect uaccess, so must be saved/restored early. if (ctxt_has_s1poe(ctxt)) @@ -33,16 +58,6 @@ static inline void __sysreg_save_user_state(struct kvm_cpu_context *ctxt) ctxt_sys_reg(ctxt, TPIDRRO_EL0) = read_sysreg(tpidrro_el0); } -static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt) -{ - struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu; - - if (!vcpu) - vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt); - - return vcpu; -} - static inline bool ctxt_has_mte(struct kvm_cpu_context *ctxt) { struct kvm_vcpu *vcpu = ctxt_to_vcpu(ctxt); @@ -139,7 +154,7 @@ static inline void __sysreg_save_el2_return_state(struct kvm_cpu_context *ctxt) static inline void __sysreg_restore_common_state(struct kvm_cpu_context *ctxt) { - write_sysreg(ctxt_sys_reg(ctxt, MDSCR_EL1), mdscr_el1); + write_sysreg(*ctxt_mdscr_el1(ctxt), mdscr_el1); // POR_EL0 can affect uaccess, so must be saved/restored early. if (ctxt_has_s1poe(ctxt))