Re: [PATCH v3 2/2] arch/powerpc/kvm: kvmppc_hv_entry: remove r4 argument
From: "Nicholas Piggin" <npiggin@gmail.com>
Date: 2023-03-21 04:16:29
Also in:
lkml
On Thu Mar 16, 2023 at 3:10 PM AEST, Kautuk Consul wrote:
kvmppc_hv_entry is called from only 2 locations within book3s_hv_rmhandlers.S. Both of those locations set r4 as HSTATE_KVM_VCPU(r13) before calling kvmppc_hv_entry. So, shift the r4 load instruction to kvmppc_hv_entry and thus modify the calling convention of this function.
Is r4 there only used for CONFIG_KVM_BOOK3S_HV_P8_TIMING? Could put it under there. Although you then lose the barrier if it's disabled, that is okay if you're sure that's the only memory operation being ordered. I'm not sure how much new work we want to put into changing this asm code, since it's POWER7/8 only. I would love to move this (and the other) KVM implementations to C like we did with P9. It's a pretty big job though. Thanks, Nick
quoted hunk ↗ jump to hunk
Signed-off-by: Kautuk Consul <redacted> --- arch/powerpc/kvm/book3s_hv_rmhandlers.S | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S index b81ba4ee0521..b61f0b2c677b 100644 --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S@@ -85,7 +85,7 @@ _GLOBAL_TOC(kvmppc_hv_entry_trampoline) RFI_TO_KERNEL kvmppc_call_hv_entry: - ld r4, HSTATE_KVM_VCPU(r13) + /* Enter guest. */ bl kvmppc_hv_entry /* Back from guest - restore host state and return to caller */@@ -352,9 +352,7 @@ kvm_secondary_got_guest: mtspr SPRN_LDBAR, r0 isync 63: - /* Order load of vcpu after load of vcore */ - lwsync - ld r4, HSTATE_KVM_VCPU(r13) + /* Enter guest. */ bl kvmppc_hv_entry /* Back from the guest, go back to nap */@@ -506,7 +504,6 @@ SYM_INNER_LABEL(kvmppc_hv_entry, SYM_L_LOCAL) /* Required state: * - * R4 = vcpu pointer (or NULL) * MSR = ~IR|DR * R13 = PACA * R1 = host R1@@ -524,6 +521,10 @@ SYM_INNER_LABEL(kvmppc_hv_entry, SYM_L_LOCAL) li r6, KVM_GUEST_MODE_HOST_HV stb r6, HSTATE_IN_GUEST(r13) + /* Order load of vcpu after load of vcore */ + lwsync + ld r4, HSTATE_KVM_VCPU(r13) + #ifdef CONFIG_KVM_BOOK3S_HV_P8_TIMING /* Store initial timestamp */ cmpdi r4, 0-- 2.39.2