On 08.11.2013, at 03:44, Liu Ping Fan <kernelfans@xxxxxxxxx> wrote:
> syscall is a very common behavior inside guest, and this patch
> optimizes the path for the emulation of BOOK3S_INTERRUPT_SYSCALL,
> so hypervisor can return to guest without heavy exit, i.e, no need
> to swap TLB, HTAB,.. etc
The syscall exit you touch here only happens when you do an sc > 0 with MSR_PR set inside the guest. The only case you realistically see this is when you run PR KVM inside of an HV KVM guest.
I don't think we should optimize for that case. Instead, we should rather try to not bounce to the 1st hypervisor in the first place in that scenario :).
Alex
>
> Signed-off-by: Liu Ping Fan <pingfank@xxxxxxxxxxxxxxxxxx>
> ---
> Compiled, but lack of bare metal, I have not tested it yet.
> ---
> arch/powerpc/kvm/book3s_hv.c | 6 ------
> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 13 ++++++++++++-
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 62a2b5a..73dc852 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -628,12 +628,6 @@ static int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
> /* hcall - punt to userspace */
> int i;
>
> - if (vcpu->arch.shregs.msr & MSR_PR) {
> - /* sc 1 from userspace - reflect to guest syscall */
> - kvmppc_book3s_queue_irqprio(vcpu, BOOK3S_INTERRUPT_SYSCALL);
> - r = RESUME_GUEST;
> - break;
> - }
> run->papr_hcall.nr = kvmppc_get_gpr(vcpu, 3);
> for (i = 0; i < 9; ++i)
> run->papr_hcall.args[i] = kvmppc_get_gpr(vcpu, 4 + i);
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index c71103b..9f626c3 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -1388,7 +1388,8 @@ kvmppc_hisi:
> hcall_try_real_mode:
> ld r3,VCPU_GPR(R3)(r9)
> andi. r0,r11,MSR_PR
> - bne guest_exit_cont
> + /* sc 1 from userspace - reflect to guest syscall */
> + bne sc_0_fast_return
> clrrdi r3,r3,2
> cmpldi r3,hcall_real_table_end - hcall_real_table
> bge guest_exit_cont
> @@ -1409,6 +1410,16 @@ hcall_try_real_mode:
> ld r11,VCPU_MSR(r4)
> b fast_guest_return
>
> +sc_0_fast_return:
> + ld r10,VCPU_PC(r9)
> + ld r11,VCPU_MSR(r9)
> + mtspr SPRN_SRR0,r10
> + mtspr SPRN_SRR1,r11
> + li r10, BOOK3S_INTERRUPT_SYSCALL
> + LOAD_REG_IMMEDIATE(r3,0xffffffff87a0ffff) /* zero 33:36,42:47 */
> + and r11,r11,r3
> + b fast_guest_return
> +
> /* We've attempted a real mode hcall, but it's punted it back
> * to userspace. We need to restore some clobbered volatiles
> * before resuming the pass-it-to-qemu path */
> --
> 1.8.1.4
>
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