Re: [PATCH v1 RESEND] arch/powerpc/kvm: Fix doorbell emulation by adding DPDES support
From: Nicholas Piggin
Date: Mon Jun 03 2024 - 01:42:45 EST
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?
> 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.
> +
> 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.
> + }
> +
> /* 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.
> 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 :)
Thanks,
Nick