Hi,
On 2023-03-21 14:15:14, Nicholas Piggin wrote: > 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. r4 is also used by the secondary_too_late label. So I decided against moving it inside the CONFIG_KVM_BOOK3S_HV_P8_TIMING #ifdef as then I would need to again load from HSTATE_KVM_VCPU(r13) in secondary_too_late. > > 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. Yeah. I was just reviewing this code and decided to send this small improvement to the mailing list. I will check with my team and ask them if we could move this implementation to C. > > Thanks, > Nick > > > > > Signed-off-by: Kautuk Consul <kcon...@linux.vnet.ibm.com> > > --- > > 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 >
