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Date: Mon, 3 Jun 2024 12:39:16 +0530
From: Gautam Menghani <gautam@linux.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: mpe@ellerman.id.au, christophe.leroy@csgroup.eu, aneesh.kumar@kernel.org,
        naveen.n.rao@linux.ibm.com, corbet@lwn.net,
        linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH v1 RESEND] arch/powerpc/kvm: Fix doorbell emulation by
 adding DPDES support
Message-ID: <r74chlv6bgs5csvuf4nxxtylmgartvibftp3xuztyfuynqetp5@ythddpzo6yfi>
References: <20240522084949.123148-1-gautam@linux.ibm.com>
 <D1Q54PY40E3B.22QS5DMQRA58N@gmail.com>
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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@vger.kernel.org
> > Signed-off-by: Gautam Menghani <gautam@linux.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