Currently VFP/SIMD registers are always saved and restored on Guest entry and exit.
This patch only saves and restores VFP/SIMD registers on Guest access. To do this cptr_el2 VFP/SIMD trap is set on Guest entry and later checked on exit. This follows the ARMv7 VFPv3 implementation. Running an informal test there are high number of exits that don't access VFP/SIMD registers. Tested on FVP Model, executed threads on host and Guest accessing VFP/SIMD registers resulting in consistent results. Signed-off-by: Mario Smarduch <[email protected]> --- arch/arm64/include/asm/kvm_arm.h | 5 +++- arch/arm64/kvm/hyp.S | 57 +++++++++++++++++++++++++++++++++++++--- 2 files changed, 57 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h index ac6fafb..7605e09 100644 --- a/arch/arm64/include/asm/kvm_arm.h +++ b/arch/arm64/include/asm/kvm_arm.h @@ -171,10 +171,13 @@ #define HSTR_EL2_TTEE (1 << 16) #define HSTR_EL2_T(x) (1 << x) +/* Hyp Coproccessor Trap Register Shifts */ +#define CPTR_EL2_TFP_SHIFT 10 + /* Hyp Coprocessor Trap Register */ #define CPTR_EL2_TCPAC (1 << 31) #define CPTR_EL2_TTA (1 << 20) -#define CPTR_EL2_TFP (1 << 10) +#define CPTR_EL2_TFP (1 << CPTR_EL2_TFP_SHIFT) /* Hyp Debug Configuration Register bits */ #define MDCR_EL2_TDRA (1 << 11) diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S index 5befd01..b3044b4 100644 --- a/arch/arm64/kvm/hyp.S +++ b/arch/arm64/kvm/hyp.S @@ -673,6 +673,24 @@ tbz \tmp, #KVM_ARM64_DEBUG_DIRTY_SHIFT, \target .endm +/* + * Check cptr VFP/SIMD accessed bit, if set VFP/SIMD not accessed by guest. + */ +.macro skip_fpsimd_state tmp, target + mrs \tmp, cptr_el2 + tbnz \tmp, #CPTR_EL2_TFP_SHIFT, \target +.endm + +/* + * Check cptr VFP/SIMD accessed bit if set, VFP/SIMD not accessed by guest. + * Also disable all cptr traps on return to host. + */ +.macro skip_fpsimd_state_reset tmp, target + mrs \tmp, cptr_el2 + msr cptr_el2, xzr + tbnz \tmp, #CPTR_EL2_TFP_SHIFT, \target +.endm + .macro compute_debug_state target // Compute debug state: If any of KDE, MDE or KVM_ARM64_DEBUG_DIRTY // is set, we do a full save/restore cycle and disable trapping. @@ -763,6 +781,7 @@ ldr x2, [x0, #VCPU_HCR_EL2] msr hcr_el2, x2 mov x2, #CPTR_EL2_TTA + orr x2, x2, #CPTR_EL2_TFP msr cptr_el2, x2 mov x2, #(1 << 15) // Trap CP15 Cr=15 @@ -785,7 +804,6 @@ .macro deactivate_traps mov x2, #HCR_RW msr hcr_el2, x2 - msr cptr_el2, xzr msr hstr_el2, xzr mrs x2, mdcr_el2 @@ -911,6 +929,30 @@ __save_fpsimd: __restore_fpsimd: restore_fpsimd ret +/* + * On Guest VFP/SIMD access, switch Guest/Host registers and reset cptr access + * bit to disable trapping. + */ +switch_to_guest_vfp: + ldr x2, =(CPTR_EL2_TTA) + msr cptr_el2, x2 + + mrs x0, tpidr_el2 + + ldr x2, [x0, #VCPU_HOST_CONTEXT] + kern_hyp_va x2 + + add x3, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS) + fpsimd_save x3, 1 + + add x2, x0, #VCPU_CONTEXT + add x3, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS) + fpsimd_restore x3, 1 + + pop x2, x3 + pop x0, x1 + + eret /* * u64 __kvm_vcpu_run(struct kvm_vcpu *vcpu); @@ -932,7 +974,6 @@ ENTRY(__kvm_vcpu_run) kern_hyp_va x2 save_host_regs - bl __save_fpsimd bl __save_sysregs compute_debug_state 1f @@ -948,7 +989,6 @@ ENTRY(__kvm_vcpu_run) add x2, x0, #VCPU_CONTEXT bl __restore_sysregs - bl __restore_fpsimd skip_debug_state x3, 1f bl __restore_debug @@ -967,7 +1007,9 @@ __kvm_vcpu_return: add x2, x0, #VCPU_CONTEXT save_guest_regs + skip_fpsimd_state x3, 1f bl __save_fpsimd +1: bl __save_sysregs skip_debug_state x3, 1f @@ -986,8 +1028,11 @@ __kvm_vcpu_return: kern_hyp_va x2 bl __restore_sysregs - bl __restore_fpsimd + /* Disable cptr VFP/SIMD access bit, skip restore if VFP not accessed */ + skip_fpsimd_state_reset x3, 1f + bl __restore_fpsimd +1: skip_debug_state x3, 1f // Clear the dirty flag for the next run, as all the state has // already been saved. Note that we nuke the whole 64bit word. @@ -1166,6 +1211,10 @@ el1_sync: // Guest trapped into EL2 mrs x1, esr_el2 lsr x2, x1, #ESR_ELx_EC_SHIFT + /* Guest accessed VFP/SIMD registers, save host, restore Guest */ + cmp x2, #ESR_ELx_EC_FP_ASIMD + b.eq switch_to_guest_vfp + cmp x2, #ESR_ELx_EC_HVC64 b.ne el1_trap -- 1.9.1 _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
