On Mon, 2017-05-29 at 20:12 +1000, Paul Mackerras wrote:
> This allows userspace (e.g. QEMU) to enable large decrementer mode
> for
> the guest when running on a POWER9 host, by setting the LPCR_LD bit
> in
> the guest LPCR value. With this, the guest exit code saves 64 bits
> of
> the guest DEC value on exit. Other places that use the guest DEC
> value check the LPCR_LD bit in the guest LPCR value, and if it is
> set,
> omit the 32-bit sign extension that would otherwise be done.
>
> This doesn't change the DEC emulation used by PR KVM because PR KVM
> is not supported on POWER9 yet.
>
> This is partly based on an earlier patch by Oliver O'Halloran.
>
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Tested with a hacked up qemu and upstream guest/host (with these
patches).
Tested-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
> ---
> arch/powerpc/include/asm/kvm_host.h | 2 +-
> arch/powerpc/kvm/book3s_hv.c | 6 ++++++
> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 29
> ++++++++++++++++++++++++-----
> arch/powerpc/kvm/emulate.c | 4 ++--
> 4 files changed, 33 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h
> b/arch/powerpc/include/asm/kvm_host.h
> index 9c51ac4..3f879c8 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -579,7 +579,7 @@ struct kvm_vcpu_arch {
> ulong mcsrr0;
> ulong mcsrr1;
> ulong mcsr;
> - u32 dec;
> + ulong dec;
> #ifdef CONFIG_BOOKE
> u32 decar;
> #endif
> diff --git a/arch/powerpc/kvm/book3s_hv.c
> b/arch/powerpc/kvm/book3s_hv.c
> index 42b7a4f..9b2eb66 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1143,6 +1143,12 @@ static void kvmppc_set_lpcr(struct kvm_vcpu
> *vcpu, u64 new_lpcr,
> mask = LPCR_DPFD | LPCR_ILE | LPCR_TC;
> if (cpu_has_feature(CPU_FTR_ARCH_207S))
> mask |= LPCR_AIL;
> + /*
> + * On POWER9, allow userspace to enable large decrementer
> for the
> + * guest, whether or not the host has it enabled.
> + */
> + if (cpu_has_feature(CPU_FTR_ARCH_300))
> + mask |= LPCR_LD;
>
> /* Broken 32-bit version of LPCR must not clear top bits */
> if (preserve_top32)
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index e390b38..3c901b5 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -920,7 +920,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
> mftb r7
> subf r3,r7,r8
> mtspr SPRN_DEC,r3
> - stw r3,VCPU_DEC(r4)
> + std r3,VCPU_DEC(r4)
>
> ld r5, VCPU_SPRG0(r4)
> ld r6, VCPU_SPRG1(r4)
> @@ -1032,7 +1032,13 @@ kvmppc_cede_reentry: /* r4 =
> vcpu, r13 = paca */
> li r0, BOOK3S_INTERRUPT_EXTERNAL
> bne cr1, 12f
> mfspr r0, SPRN_DEC
> - cmpwi r0, 0
> +BEGIN_FTR_SECTION
> + /* On POWER9 check whether the guest has large decrementer
> enabled */
> + andis. r8, r8, LPCR_LD@h
> + bne 15f
> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> + extsw r0, r0
> +15: cmpdi r0, 0
> li r0, BOOK3S_INTERRUPT_DECREMENTER
> bge 5f
>
> @@ -1459,12 +1465,18 @@ mc_cont:
> mtspr SPRN_SPURR,r4
>
> /* Save DEC */
> + ld r3, HSTATE_KVM_VCORE(r13)
> mfspr r5,SPRN_DEC
> mftb r6
> + /* On P9, if the guest has large decr enabled, don't sign
> extend */
> +BEGIN_FTR_SECTION
> + ld r4, VCORE_LPCR(r3)
> + andis. r4, r4, LPCR_LD@h
> + bne 16f
> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> extsw r5,r5
> - add r5,r5,r6
> +16: add r5,r5,r6
> /* r5 is a guest timebase value here, convert to host TB */
> - ld r3,HSTATE_KVM_VCORE(r13)
> ld r4,VCORE_TB_OFFSET(r3)
> subf r5,r4,r5
> std r5,VCPU_DEC_EXPIRES(r9)
> @@ -2376,8 +2388,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
> mfspr r3, SPRN_DEC
> mfspr r4, SPRN_HDEC
> mftb r5
> +BEGIN_FTR_SECTION
> + /* On P9 check whether the guest has large decrementer mode
> enabled */
> + ld r6, HSTATE_KVM_VCORE(r13)
> + ld r6, VCORE_LPCR(r6)
> + andis. r6, r6, LPCR_LD@h
> + bne 68f
> +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> extsw r3, r3
> - EXTEND_HDEC(r4)
> +68: EXTEND_HDEC(r4)
> cmpd r3, r4
> ble 67f
> mtspr SPRN_DEC, r4
> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
> index c873ffe..4d8b4d6 100644
> --- a/arch/powerpc/kvm/emulate.c
> +++ b/arch/powerpc/kvm/emulate.c
> @@ -39,7 +39,7 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu)
> unsigned long dec_nsec;
> unsigned long long dec_time;
>
> - pr_debug("mtDEC: %x\n", vcpu->arch.dec);
> + pr_debug("mtDEC: %lx\n", vcpu->arch.dec);
> hrtimer_try_to_cancel(&vcpu->arch.dec_timer);
>
> #ifdef CONFIG_PPC_BOOK3S
> @@ -109,7 +109,7 @@ static int kvmppc_emulate_mtspr(struct kvm_vcpu
> *vcpu, int sprn, int rs)
> case SPRN_TBWU: break;
>
> case SPRN_DEC:
> - vcpu->arch.dec = spr_val;
> + vcpu->arch.dec = (u32) spr_val;
> kvmppc_emulate_dec(vcpu);
> break;
>
