On 30/08/16 10:55, Christoffer Dall wrote: > On Mon, Aug 29, 2016 at 10:51:14PM -0500, Shanker Donthineni wrote: >> We are doing an unnecessary stack push/pop operation when restoring >> the guest registers x0-x18 in __guest_enter(). This patch saves the >> two instructions by using x18 as a base register. No need to store >> the vcpu context pointer in stack because it is redundant, the same >> information is available in tpidr_el2. The function __guest_exit() >> prototype is simplified and caller pushes the regs x0-x1 to stack >> instead of regs x0-x3. >> >> Signed-off-by: Shanker Donthineni <shankerd@xxxxxxxxxxxxxx> > > This looks reasonable to me: > > Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> > > Unless Marc has any insight into this having a negative effect on ARM > CPUs, I'll go ahead an merge this. I've given it a go on Seattle, and couldn't observe any difference with the original code, which is pretty good news! I have some comments below, though: > > -Christoffer > >> --- >> Changes since v1: >> Incorporated Cristoffer suggestions. >> __guest_exit prototype is changed to 'void __guest_exit(u64 reason, struct kvm_vcpu *vcpu)'. >> >> arch/arm64/kvm/hyp/entry.S | 101 +++++++++++++++++++++-------------------- >> arch/arm64/kvm/hyp/hyp-entry.S | 11 +++-- >> 2 files changed, 57 insertions(+), 55 deletions(-) >> >> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S >> index ce9e5e5..f70489a 100644 >> --- a/arch/arm64/kvm/hyp/entry.S >> +++ b/arch/arm64/kvm/hyp/entry.S >> @@ -55,75 +55,76 @@ >> */ >> ENTRY(__guest_enter) >> // x0: vcpu >> - // x1: host/guest context >> - // x2-x18: clobbered by macros >> + // x1: host context >> + // x2-x17: clobbered by macros >> + // x18: guest context >> >> // Store the host regs >> save_callee_saved_regs x1 >> >> - // Preserve vcpu & host_ctxt for use at exit time >> - stp x0, x1, [sp, #-16]! >> + // Store the host_ctxt for use at exit time >> + str x1, [sp, #-16]! >> >> - add x1, x0, #VCPU_CONTEXT >> + add x18, x0, #VCPU_CONTEXT >> >> - // Prepare x0-x1 for later restore by pushing them onto the stack >> - ldp x2, x3, [x1, #CPU_XREG_OFFSET(0)] >> - stp x2, x3, [sp, #-16]! >> + // Restore guest regs x0-x17 >> + ldp x0, x1, [x18, #CPU_XREG_OFFSET(0)] >> + ldp x2, x3, [x18, #CPU_XREG_OFFSET(2)] >> + ldp x4, x5, [x18, #CPU_XREG_OFFSET(4)] >> + ldp x6, x7, [x18, #CPU_XREG_OFFSET(6)] >> + ldp x8, x9, [x18, #CPU_XREG_OFFSET(8)] >> + ldp x10, x11, [x18, #CPU_XREG_OFFSET(10)] >> + ldp x12, x13, [x18, #CPU_XREG_OFFSET(12)] >> + ldp x14, x15, [x18, #CPU_XREG_OFFSET(14)] >> + ldp x16, x17, [x18, #CPU_XREG_OFFSET(16)] >> >> - // x2-x18 >> - ldp x2, x3, [x1, #CPU_XREG_OFFSET(2)] >> - ldp x4, x5, [x1, #CPU_XREG_OFFSET(4)] >> - ldp x6, x7, [x1, #CPU_XREG_OFFSET(6)] >> - ldp x8, x9, [x1, #CPU_XREG_OFFSET(8)] >> - ldp x10, x11, [x1, #CPU_XREG_OFFSET(10)] >> - ldp x12, x13, [x1, #CPU_XREG_OFFSET(12)] >> - ldp x14, x15, [x1, #CPU_XREG_OFFSET(14)] >> - ldp x16, x17, [x1, #CPU_XREG_OFFSET(16)] >> - ldr x18, [x1, #CPU_XREG_OFFSET(18)] >> + // Restore guest regs x19-x29, lr >> + restore_callee_saved_regs x18 >> >> - // x19-x29, lr >> - restore_callee_saved_regs x1 >> - >> - // Last bits of the 64bit state >> - ldp x0, x1, [sp], #16 >> + // Restore guest reg x18 >> + ldr x18, [x18, #CPU_XREG_OFFSET(18)] >> >> // Do not touch any register after this! >> eret >> ENDPROC(__guest_enter) >> >> +/* >> + * void __guest_exit(u64 exit_reason, struct kvm_vcpu *vcpu); >> + */ I'm not sure this comment makes much sense as it stands. This is not a C function by any stretch of the imagination, but the continuation of __guest_enter. The calling convention is not the C one at all (see how the stack is involved), and caller-saved registers are going to be clobbered. >> ENTRY(__guest_exit) >> - // x0: vcpu >> - // x1: return code >> - // x2-x3: free >> - // x4-x29,lr: vcpu regs >> - // vcpu x0-x3 on the stack >> - >> - add x2, x0, #VCPU_CONTEXT >> - >> - stp x4, x5, [x2, #CPU_XREG_OFFSET(4)] >> - stp x6, x7, [x2, #CPU_XREG_OFFSET(6)] >> - stp x8, x9, [x2, #CPU_XREG_OFFSET(8)] >> - stp x10, x11, [x2, #CPU_XREG_OFFSET(10)] >> - stp x12, x13, [x2, #CPU_XREG_OFFSET(12)] >> - stp x14, x15, [x2, #CPU_XREG_OFFSET(14)] >> - stp x16, x17, [x2, #CPU_XREG_OFFSET(16)] >> - str x18, [x2, #CPU_XREG_OFFSET(18)] >> - >> - ldp x6, x7, [sp], #16 // x2, x3 >> - ldp x4, x5, [sp], #16 // x0, x1 >> - >> - stp x4, x5, [x2, #CPU_XREG_OFFSET(0)] >> - stp x6, x7, [x2, #CPU_XREG_OFFSET(2)] >> + // x0: return code >> + // x1: vcpu >> + // x2-x29,lr: vcpu regs >> + // vcpu x0-x1 on the stack >> + >> + add x1, x1, #VCPU_CONTEXT >> + >> + // Store the guest regs x2 and x3 >> + stp x2, x3, [x1, #CPU_XREG_OFFSET(2)] >> + >> + // Retrieve the guest regs x0-x1 from the stack >> + ldp x2, x3, [sp], #16 // x0, x1 >> + >> + // Store the guest regs x0-x1 and x4-x18 >> + stp x2, x3, [x1, #CPU_XREG_OFFSET(0)] >> + stp x4, x5, [x1, #CPU_XREG_OFFSET(4)] >> + stp x6, x7, [x1, #CPU_XREG_OFFSET(6)] >> + stp x8, x9, [x1, #CPU_XREG_OFFSET(8)] >> + stp x10, x11, [x1, #CPU_XREG_OFFSET(10)] >> + stp x12, x13, [x1, #CPU_XREG_OFFSET(12)] >> + stp x14, x15, [x1, #CPU_XREG_OFFSET(14)] >> + stp x16, x17, [x1, #CPU_XREG_OFFSET(16)] >> + str x18, [x1, #CPU_XREG_OFFSET(18)] >> + >> + // Store the guest regs x19-x29, lr >> + save_callee_saved_regs x1 >> >> - save_callee_saved_regs x2 >> + // Restore the host_ctxt from the stack >> + ldr x2, [sp], #16 >> >> - // Restore vcpu & host_ctxt from the stack >> - // (preserving return code in x1) >> - ldp x0, x2, [sp], #16 >> // Now restore the host regs >> restore_callee_saved_regs x2 >> >> - mov x0, x1 >> ret >> ENDPROC(__guest_exit) >> >> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S >> index f6d9694..06e8b3b 100644 >> --- a/arch/arm64/kvm/hyp/hyp-entry.S >> +++ b/arch/arm64/kvm/hyp/hyp-entry.S >> @@ -121,14 +121,15 @@ el1_trap: >> cmp x2, #ESR_ELx_EC_FP_ASIMD >> b.eq __fpsimd_guest_restore >> >> - mrs x0, tpidr_el2 >> - mov x1, #ARM_EXCEPTION_TRAP >> + ldp x2, x3, [sp], #16 >> + mrs x1, tpidr_el2 >> + mov x0, #ARM_EXCEPTION_TRAP >> b __guest_exit >> >> el1_irq: >> - save_x0_to_x3 So the save_x0_to_x3 macro now only has one single user (and so does restore_x0_to_x3). Should we consider inline it? >> - mrs x0, tpidr_el2 >> - mov x1, #ARM_EXCEPTION_IRQ >> + stp x0, x1, [sp, #-16]! >> + mrs x1, tpidr_el2 >> + mov x0, #ARM_EXCEPTION_IRQ >> b __guest_exit >> >> ENTRY(__hyp_do_panic) >> -- >> Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc. >> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. >> > Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
