Hi, On 2023-03-16 14:39:08, Michael Ellerman wrote: > Kautuk Consul <kcon...@linux.vnet.ibm.com> writes: > > On 2023-03-15 15:48:53, Michael Ellerman wrote: > >> Kautuk Consul <kcon...@linux.vnet.ibm.com> writes: > >> > 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. > >> > > >> > Signed-off-by: Kautuk Consul <kcon...@linux.vnet.ibm.com> > >> > --- > >> > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 9 ++++----- > >> > 1 file changed, 4 insertions(+), 5 deletions(-) > >> > > >> > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > >> > b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > >> > index b81ba4ee0521..da9a15db12fe 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 > >> > >> Where did this barrier go? > >> > >> I don't see that it's covered by any existing barriers in > >> kvmppc_hv_entry, and you don't add it back anywhere. > > > > My concept about this is that since now the call to kvmppc_hv_entry > > is first taken before the load to r4 shouldn't the pending load in the > > pipeline of the HSTATE_KVM_VCORE as per the earlier comment be ordered > > anyway > > before-hand ? > > No. > > > Or do you mean to say that pending loads may not be > > cleared/flushed across the "bl <funcname>" boundary ? > > Right. > > The "bl" imposes no ordering on loads before or after it. > > In general nothing orders two independant loads, other than a barrier. > > cheers
Okay, I will post a patch v3 with lwsync before the load to r4 in kvmppc_hv_entry. Thanks.
