On Fri, Nov 08, 2013 at 10:44:16AM +0800, Liu Ping Fan 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 Many interrupts that are caused by guest code go directly to the guest and don't come to the hypervisor at all. That includes system call (sc 0), alignment interrupts, program interrupts, SLB miss interrupts, etc. See section 6.5 of Book 3S of the Power ISA specification; all the interrupts with '-' in the 'HV' column of the table there get delivered directly to the guest when they occur inside a guest. > --- 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 Discrepancy between comment and code here. In fact we would only take the branch for a sc 1 instruction in userspace, which occurs when a PR KVM guest nested inside a HV KVM guest does a hypercall (i.e., not for normal system calls). It is probably worthwhile to speed those up. > +sc_0_fast_return: > + ld r10,VCPU_PC(r9) > + ld r11,VCPU_MSR(r9) r11 must already contain this since you just did andi. r0,r11,MSR_PR. In fact r10 already contains VCPU_PC(r9) at this point also, though that is not so obvious. > + 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 This is not correct, since you don't even clear PR. In fact what you need is to load up MSR_SF | MSR_ME, though that value changes with little-endian support and changes again with transactional memory support for POWER8. There is an idiom for loading that MSR value, which is: li r11, (MSR_ME << 1) | 1 /* synthesize MSR_SF | MSR_ME */ rotldi r11, r11, 63 which you could use for now, but it will need to be changed when Anton's LE patch gets accepted. Paul. -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
