| Message ID | 1472529074-19261-1-git-send-email-shankerd@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@codeaurora.org> This looks reasonable to me: Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Unless Marc has any insight into this having a negative effect on ARM CPUs, I'll go ahead an merge this. -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); > + */ > 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 > - 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. >
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@codeaurora.org> > > This looks reasonable to me: > > Reviewed-by: Christoffer Dall <christoffer.dall@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 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.
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 <shankerd@codeaurora.org> >> This looks reasonable to me: >> >> Reviewed-by: Christoffer Dall <christoffer.dall@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 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. 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, 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? 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_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.
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); + */ 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 - 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)
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@codeaurora.org> --- 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(-)