Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH v2 2/2] arch/powerpc/kvm: kvmppc_hv_entry: remove r4 argument | Date | Thu, 16 Mar 2023 14:39:08 +1100 |
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Kautuk Consul <kconsul@linux.vnet.ibm.com> writes: > On 2023-03-15 15:48:53, Michael Ellerman wrote: >> Kautuk Consul <kconsul@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 <kconsul@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
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