From: Michael Ellerman <mpe@ellerman•id.au>
To: Kautuk Consul <kconsul@linux•vnet.ibm.com>
Cc: Fabiano Rosas <farosas@linux•ibm.com>,
Alexey Kardashevskiy <aik@ozlabs•ru>,
linux-kernel@vger•kernel.org,
Sathvika Vasireddy <sv@linux•ibm.com>,
Nicholas Piggin <npiggin@gmail•com>,
"Naveen N. Rao" <naveen.n.rao@linux•vnet.ibm.com>,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH v2 2/2] arch/powerpc/kvm: kvmppc_hv_entry: remove r4 argument
Date: Thu, 16 Mar 2023 14:39:08 +1100 [thread overview]
Message-ID: <87wn3hmkkj.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <ZBFVAxAFsUJtuzEy@li-a450e7cc-27df-11b2-a85c-b5a9ac31e8ef.ibm.com>
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
next prev parent reply other threads:[~2023-03-16 3:40 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 12:37 [PATCH v2 0/2] Improving calls to kvmppc_hv_entry Kautuk Consul
2023-03-06 12:37 ` [PATCH v2 1/2] arch/powerpc/kvm: kvmppc_hv_entry: remove .global scope Kautuk Consul
2023-03-06 12:37 ` [PATCH v2 2/2] arch/powerpc/kvm: kvmppc_hv_entry: remove r4 argument Kautuk Consul
2023-03-15 4:48 ` Michael Ellerman
2023-03-15 5:17 ` Kautuk Consul
2023-03-15 5:37 ` Kautuk Consul
2023-03-16 3:39 ` Michael Ellerman [this message]
2023-03-16 3:40 ` Michael Ellerman
2023-03-16 3:49 ` Kautuk Consul
2023-03-13 5:39 ` [PATCH v2 0/2] Improving calls to kvmppc_hv_entry Kautuk Consul
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