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Date: Mon, 03 Jun 2024 18:06:34 +1000
From: "Nicholas Piggin" <npiggin@...il.com>
To: "Gautam Menghani" <gautam@...ux.ibm.com>
Cc: <mpe@...erman.id.au>, <christophe.leroy@...roup.eu>,
<aneesh.kumar@...nel.org>, <naveen.n.rao@...ux.ibm.com>, <corbet@....net>,
<linuxppc-dev@...ts.ozlabs.org>, <kvm@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<stable@...r.kernel.org>
Subject: Re: [PATCH v1 RESEND] arch/powerpc/kvm: Fix doorbell emulation by
adding DPDES support
On Mon Jun 3, 2024 at 5:09 PM AEST, Gautam Menghani wrote:
> On Mon, Jun 03, 2024 at 03:42:22PM GMT, Nicholas Piggin wrote:
> > On Wed May 22, 2024 at 6:49 PM AEST, Gautam Menghani wrote:
> > > Doorbell emulation is broken for KVM on PowerVM guests as support for
> > > DPDES was not added in the initial patch series. Due to this, a KVM on
> > > PowerVM guest cannot be booted with the XICS interrupt controller as
> > > doorbells are to be setup in the initial probe path when using XICS
> > > (pSeries_smp_probe()). Add DPDES support in the host KVM code to fix
> > > doorbell emulation.
> >
> > This is broken when the KVM guest has SMT > 1? Or is it broken for SMT=1
> > as well? Can you explain a bit more of what breaks if it's the latter?
>
> Yes, doorbells are only setup when we use SMT>1 and interrupt controller
> is XICS. So without this patch, L2 KOP guest with XICS IC mode and SMT>1
> does not boot. SMT 1 is fine in all cases.
Okay good. Make that clear in the changelog, ideally if you can give
a recipe the reader is able to recreate is good too, (e.g., run the
guest machine with -smp 4,threads=4 and xive=off boot parameter).
> > > Fixes: 6ccbbc33f06a ("KVM: PPC: Add helper library for Guest State Buffers")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
> > > ---
> > > v1 -> v1 resend:
> > > 1. Add the stable tag
> > >
> > > Documentation/arch/powerpc/kvm-nested.rst | 4 +++-
> > > arch/powerpc/include/asm/guest-state-buffer.h | 3 ++-
> > > arch/powerpc/include/asm/kvm_book3s.h | 1 +
> > > arch/powerpc/kvm/book3s_hv.c | 14 +++++++++++++-
> > > arch/powerpc/kvm/book3s_hv_nestedv2.c | 7 +++++++
> > > arch/powerpc/kvm/test-guest-state-buffer.c | 2 +-
> > > 6 files changed, 27 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/Documentation/arch/powerpc/kvm-nested.rst b/Documentation/arch/powerpc/kvm-nested.rst
> > > index 630602a8aa00..5defd13cc6c1 100644
> > > --- a/Documentation/arch/powerpc/kvm-nested.rst
> > > +++ b/Documentation/arch/powerpc/kvm-nested.rst
> > > @@ -546,7 +546,9 @@ table information.
> > > +--------+-------+----+--------+----------------------------------+
> > > | 0x1052 | 0x08 | RW | T | CTRL |
> > > +--------+-------+----+--------+----------------------------------+
> > > -| 0x1053-| | | | Reserved |
> > > +| 0x1053 | 0x08 | RW | T | DPDES |
> > > ++--------+-------+----+--------+----------------------------------+
> > > +| 0x1054-| | | | Reserved |
> > > | 0x1FFF | | | | |
> > > +--------+-------+----+--------+----------------------------------+
> > > | 0x2000 | 0x04 | RW | T | CR |
> > > diff --git a/arch/powerpc/include/asm/guest-state-buffer.h b/arch/powerpc/include/asm/guest-state-buffer.h
> > > index 808149f31576..d107abe1468f 100644
> > > --- a/arch/powerpc/include/asm/guest-state-buffer.h
> > > +++ b/arch/powerpc/include/asm/guest-state-buffer.h
> > > @@ -81,6 +81,7 @@
> > > #define KVMPPC_GSID_HASHKEYR 0x1050
> > > #define KVMPPC_GSID_HASHPKEYR 0x1051
> > > #define KVMPPC_GSID_CTRL 0x1052
> > > +#define KVMPPC_GSID_DPDES 0x1053
> > >
> > > #define KVMPPC_GSID_CR 0x2000
> > > #define KVMPPC_GSID_PIDR 0x2001
> > > @@ -110,7 +111,7 @@
> > > #define KVMPPC_GSE_META_COUNT (KVMPPC_GSE_META_END - KVMPPC_GSE_META_START + 1)
> > >
> > > #define KVMPPC_GSE_DW_REGS_START KVMPPC_GSID_GPR(0)
> > > -#define KVMPPC_GSE_DW_REGS_END KVMPPC_GSID_CTRL
> > > +#define KVMPPC_GSE_DW_REGS_END KVMPPC_GSID_DPDES
> > > #define KVMPPC_GSE_DW_REGS_COUNT \
> > > (KVMPPC_GSE_DW_REGS_END - KVMPPC_GSE_DW_REGS_START + 1)
> > >
> > > diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
> > > index 3e1e2a698c9e..10618622d7ef 100644
> > > --- a/arch/powerpc/include/asm/kvm_book3s.h
> > > +++ b/arch/powerpc/include/asm/kvm_book3s.h
> > > @@ -594,6 +594,7 @@ static inline u##size kvmppc_get_##reg(struct kvm_vcpu *vcpu) \
> > >
> > >
> > > KVMPPC_BOOK3S_VCORE_ACCESSOR(vtb, 64, KVMPPC_GSID_VTB)
> > > +KVMPPC_BOOK3S_VCORE_ACCESSOR(dpdes, 64, KVMPPC_GSID_DPDES)
> > > KVMPPC_BOOK3S_VCORE_ACCESSOR_GET(arch_compat, 32, KVMPPC_GSID_LOGICAL_PVR)
> > > KVMPPC_BOOK3S_VCORE_ACCESSOR_GET(lpcr, 64, KVMPPC_GSID_LPCR)
> > > KVMPPC_BOOK3S_VCORE_ACCESSOR_SET(tb_offset, 64, KVMPPC_GSID_TB_OFFSET)
> > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> > > index 35cb014a0c51..cf285e5153ba 100644
> > > --- a/arch/powerpc/kvm/book3s_hv.c
> > > +++ b/arch/powerpc/kvm/book3s_hv.c
> > > @@ -4116,6 +4116,11 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
> > > int trap;
> > > long rc;
> > >
> > > + if (vcpu->arch.doorbell_request) {
> > > + vcpu->arch.doorbell_request = 0;
> > > + kvmppc_set_dpdes(vcpu, 1);
> > > + }
> >
> > This probably looks okay... hmm, is the v1 KVM emulating doorbells
> > correctly for SMT L2 guests? I wonder if doorbell emulation isn't
> > broken there too because the L1 code looks to be passing in vc->dpdes
> > but all the POWER9 emulation code uses doorbell_request.
> >
>
> Yes launching SMT L2 on V1 API fails with a kernel Oops, I'll see if I
> can fix that as well.
Okay then I didn't miss something. Thanks v1 fix would be good too.
I think it should look something like putting doorbell_request into
hv_guest_state->dpdes that make the H_ENTER_NESTED call with.
For v1 you will need to restore the state back from dpdes back to
doorbell_request on exit, because the L0 doesn't keep it for you.
Thanks,
Nick
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