Re: [PATCH v1 RESEND] arch/powerpc/kvm: Fix doorbell emulation by adding DPDES support

[Nicholas Piggin]

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@xxxxxxxxxxxxxxx
> > > Signed-off-by: Gautam Menghani <gautam@xxxxxxxxxxxxx>
> > > ---
> > > 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