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Date: Mon, 3 Jun 2024 12:39:16 +0530
From: Gautam Menghani <gautam@...ux.ibm.com>
To: Nicholas Piggin <npiggin@...il.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 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.
>
> > 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.
> > +
> > io = &vcpu->arch.nestedv2_io;
> >
> > msr = mfmsr();
> > @@ -4278,9 +4283,16 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
> > if (kvmhv_on_pseries()) {
> > if (kvmhv_is_nestedv1())
> > trap = kvmhv_vcpu_entry_p9_nested(vcpu, time_limit, lpcr, tb);
> > - else
> > + else {
> > trap = kvmhv_vcpu_entry_nestedv2(vcpu, time_limit, lpcr, tb);
> >
> > + /* Remember doorbell if it is pending */
> > + if (kvmppc_get_dpdes(vcpu)) {
> > + vcpu->arch.doorbell_request = 1;
> > + kvmppc_set_dpdes(vcpu, 0);
> > + }
>
> This is adding an extra get state for every entry, not good. I don't
> think it's actually needed though. I don't think the L1 cares at this
> stage what the L2 DPDES state is. So you sholud be able to drop this
> hunk.
>
Yes ok.
> > + }
> > +
> > /* H_CEDE has to be handled now, not later */
> > if (trap == BOOK3S_INTERRUPT_SYSCALL && !nested &&
> > kvmppc_get_gpr(vcpu, 3) == H_CEDE) {
> > diff --git a/arch/powerpc/kvm/book3s_hv_nestedv2.c b/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > index 8e6f5355f08b..36863fff2a99 100644
> > --- a/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > +++ b/arch/powerpc/kvm/book3s_hv_nestedv2.c
> > @@ -311,6 +311,10 @@ static int gs_msg_ops_vcpu_fill_info(struct kvmppc_gs_buff *gsb,
> > rc = kvmppc_gse_put_u64(gsb, iden,
> > vcpu->arch.vcore->vtb);
> > break;
> > + case KVMPPC_GSID_DPDES:
> > + rc = kvmppc_gse_put_u64(gsb, iden,
> > + vcpu->arch.vcore->dpdes);
> > + break;
> > case KVMPPC_GSID_LPCR:
> > rc = kvmppc_gse_put_u64(gsb, iden,
> > vcpu->arch.vcore->lpcr);
> > @@ -543,6 +547,9 @@ static int gs_msg_ops_vcpu_refresh_info(struct kvmppc_gs_msg *gsm,
> > case KVMPPC_GSID_VTB:
> > vcpu->arch.vcore->vtb = kvmppc_gse_get_u64(gse);
> > break;
> > + case KVMPPC_GSID_DPDES:
> > + vcpu->arch.vcore->dpdes = kvmppc_gse_get_u64(gse);
> > + break;
> > case KVMPPC_GSID_LPCR:
> > vcpu->arch.vcore->lpcr = kvmppc_gse_get_u64(gse);
> > break;
>
> I would split all the wiring up of the DPDES GSID stuff into its own
> patch, it obviously looks fine.
>
Noted, will do.
> > diff --git a/arch/powerpc/kvm/test-guest-state-buffer.c b/arch/powerpc/kvm/test-guest-state-buffer.c
> > index 4720b8dc8837..91ae660cfe21 100644
> > --- a/arch/powerpc/kvm/test-guest-state-buffer.c
> > +++ b/arch/powerpc/kvm/test-guest-state-buffer.c
> > @@ -151,7 +151,7 @@ static void test_gs_bitmap(struct kunit *test)
> > i++;
> > }
> >
> > - for (u16 iden = KVMPPC_GSID_GPR(0); iden <= KVMPPC_GSID_CTRL; iden++) {
> > + for (u16 iden = KVMPPC_GSID_GPR(0); iden <= KVMPPC_GSID_DPDES; iden++) {
> > kvmppc_gsbm_set(&gsbm, iden);
> > kvmppc_gsbm_set(&gsbm1, iden);
> > KUNIT_EXPECT_TRUE(test, kvmppc_gsbm_test(&gsbm, iden));
>
> It would be good to have a _LAST define for such loops. It's very easy
> to miss when adding KVMPPC_GSID_DPDES that you need to grep for
> KVMPPC_GSID_CTRL. Very easy to see that you need to update _LAST.
>
> You just need to work out a good name for it since there's a few
> "namespaces" of numbers with similar prefix. Good luck :)
>
Well we already have a "KVMPPC_GSE_DW_REGS_END" defined, just missed to
use that.
> Thanks,
> Nick
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