Hi Marc,
On 08/30/2016 05:54 AM, Marc Zyngier wrote:
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 <shank...@codeaurora.org>This looks reasonable to me: Reviewed-by: Christoffer Dall <christoffer.d...@linaro.org> 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 regssave_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.
I'll remove this confusing comments.
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, x1ret ENDPROC(__guest_exit)diff --git a/arch/arm64/kvm/hyp/hyp-entry.Sb/arch/arm64/kvm/hyp/hyp-entry.Sindex 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_exitel1_irq:- save_x0_to_x3So the save_x0_to_x3 macro now only has one single user (and so does restore_x0_to_x3). Should we consider inline it?
Sure, I'll change to inline in v3 patch.
- 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_exitENTRY(__hyp_do_panic)-- Qualcomm Datacenter Technologies, Inc. on behalf of the QualcommTechnologies, Inc.Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, aLinux Foundation Collaborative Project. Thanks, M.
-- Shanker Donthineni Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
