KVM: arm64: Invoke FPSIMD context switch trap from C

The conversion of the FPSIMD context switch trap code to C has added
some overhead to calling it, due to the need to save registers that
the procedure call standard defines as caller-saved.

So, perhaps it is no longer worth invoking this trap handler quite
so early.

Instead, we can invoke it from fixup_guest_exit(), with little
likelihood of increasing the overhead much further.

As a convenience, this patch gives __hyp_switch_fpsimd() the same
return semantics fixup_guest_exit().  For now there is no
possibility of a spurious FPSIMD trap, so the function always
returns true, but this allows it to be tail-called with a single
return statement.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 40f349bc1079fb1d5beb08f4a678f3815c33f855..fad1e164fe4883fc3be8f212fc22ebe3dc28e355 100644 (file)
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -166,33 +166,3 @@ abort_guest_exit_end:
        orr     x0, x0, x5
 1:     ret
 ENDPROC(__guest_exit)
-
-ENTRY(__fpsimd_guest_restore)
-       // x0: esr
-       // x1: vcpu
-       // x2-x29,lr: vcpu regs
-       // vcpu x0-x1 on the stack
-       stp     x2, x3, [sp, #-144]!
-       stp     x4, x5, [sp, #16]
-       stp     x6, x7, [sp, #32]
-       stp     x8, x9, [sp, #48]
-       stp     x10, x11, [sp, #64]
-       stp     x12, x13, [sp, #80]
-       stp     x14, x15, [sp, #96]
-       stp     x16, x17, [sp, #112]
-       stp     x18, lr, [sp, #128]
-
-       bl      __hyp_switch_fpsimd
-
-       ldp     x4, x5, [sp, #16]
-       ldp     x6, x7, [sp, #32]
-       ldp     x8, x9, [sp, #48]
-       ldp     x10, x11, [sp, #64]
-       ldp     x12, x13, [sp, #80]
-       ldp     x14, x15, [sp, #96]
-       ldp     x16, x17, [sp, #112]
-       ldp     x18, lr, [sp, #128]
-       ldp     x0, x1, [sp, #144]
-       ldp     x2, x3, [sp], #160
-       eret
-ENDPROC(__fpsimd_guest_restore)

diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index bffece27b5c109061ef801277319f6b0a2d0e790..753b9d213651af6b2b56ee66709436c9ea23d2db 100644 (file)
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -113,25 +113,6 @@ el1_hvc_guest:
 
 el1_trap:
        get_vcpu_ptr    x1, x0
-
-       mrs             x0, esr_el2
-       lsr             x0, x0, #ESR_ELx_EC_SHIFT
-       /*
-        * x0: ESR_EC
-        * x1: vcpu pointer
-        */
-
-       /*
-        * We trap the first access to the FP/SIMD to save the host context
-        * and restore the guest context lazily.
-        * If FP/SIMD is not implemented, handle the trap and inject an
-        * undefined instruction exception to the guest.
-        */
-alternative_if_not ARM64_HAS_NO_FPSIMD
-       cmp     x0, #ESR_ELx_EC_FP_ASIMD
-       b.eq    __fpsimd_guest_restore
-alternative_else_nop_endif
-
        mov     x0, #ARM_EXCEPTION_TRAP
        b       __guest_exit
 

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 4fbee9502162bfb9fd3b41adcd2a836f26050a91..2d45bd719a5dfba78a81e36bf25cc4b72c42541b 100644 (file)
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -328,8 +328,7 @@ static bool __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
        }
 }
 
-void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused,
-                                   struct kvm_vcpu *vcpu)
+static bool __hyp_text __hyp_switch_fpsimd(struct kvm_vcpu *vcpu)
 {
        struct user_fpsimd_state *host_fpsimd = vcpu->arch.host_fpsimd_state;
 
@@ -369,6 +368,8 @@ void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused,
                             fpexc32_el2);
 
        vcpu->arch.flags |= KVM_ARM64_FP_ENABLED;
+
+       return true;
 }
 
 /*
@@ -390,6 +391,16 @@ static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
        if (*exit_code != ARM_EXCEPTION_TRAP)
                goto exit;
 
+       /*
+        * We trap the first access to the FP/SIMD to save the host context
+        * and restore the guest context lazily.
+        * If FP/SIMD is not implemented, handle the trap and inject an
+        * undefined instruction exception to the guest.
+        */
+       if (system_supports_fpsimd() &&
+           kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_FP_ASIMD)
+               return __hyp_switch_fpsimd(vcpu);
+
        if (!__populate_fault_info(vcpu))
                return true;