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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>
This commit is contained in:
Dave Martin 2018-05-02 14:18:02 +01:00 committed by Marc Zyngier
parent 7846b3119e
commit cf412b0070
3 changed files with 13 additions and 51 deletions
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30
arch/arm64/kvm/hyp/entry.S
View File

@ -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)

19
arch/arm64/kvm/hyp/hyp-entry.S
View File

@ -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

15
arch/arm64/kvm/hyp/switch.c
View File

@ -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;