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Message-ID: <874kiqy82t.fsf@linux.ibm.com> Date: Fri, 05 Feb 2021 10:09:46 -0300 From: Fabiano Rosas <farosas@...ux.ibm.com> To: Leonardo Bras <leobras.c@...il.com>, Paul Mackerras <paulus@...abs.org>, Michael Ellerman <mpe@...erman.id.au>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Christophe Leroy <christophe.leroy@...roup.eu>, Athira Rajeev <atrajeev@...ux.vnet.ibm.com>, "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>, Leonardo Bras <leobras.c@...il.com>, Jordan Niethe <jniethe5@...il.com>, Nicholas Piggin <npiggin@...il.com>, Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Geert Uytterhoeven <geert+renesas@...der.be> Cc: kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 1/1] powerpc/kvm: Save Timebase Offset to fix sched_clock() while running guest code. Leonardo Bras <leobras.c@...il.com> writes: > Before guest entry, TBU40 register is changed to reflect guest timebase. > After exitting guest, the register is reverted to it's original value. > > If one tries to get the timestamp from host between those changes, it > will present an incorrect value. > > An example would be trying to add a tracepoint in > kvmppc_guest_entry_inject_int(), which depending on last tracepoint > acquired could actually cause the host to crash. > > Save the Timebase Offset to PACA and use it on sched_clock() to always > get the correct timestamp. > > Signed-off-by: Leonardo Bras <leobras.c@...il.com> > Suggested-by: Paul Mackerras <paulus@...abs.org> > --- > Changes since v1: > - Subtracts offset only when CONFIG_KVM_BOOK3S_HANDLER and > CONFIG_PPC_BOOK3S_64 are defined. > --- > arch/powerpc/include/asm/kvm_book3s_asm.h | 1 + > arch/powerpc/kernel/asm-offsets.c | 1 + > arch/powerpc/kernel/time.c | 8 +++++++- > arch/powerpc/kvm/book3s_hv.c | 2 ++ > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 2 ++ > 5 files changed, 13 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/kvm_book3s_asm.h b/arch/powerpc/include/asm/kvm_book3s_asm.h > index 078f4648ea27..e2c12a10eed2 100644 > --- a/arch/powerpc/include/asm/kvm_book3s_asm.h > +++ b/arch/powerpc/include/asm/kvm_book3s_asm.h > @@ -131,6 +131,7 @@ struct kvmppc_host_state { > u64 cfar; > u64 ppr; > u64 host_fscr; > + u64 tb_offset; /* Timebase offset: keeps correct > timebase while on guest */ Couldn't you use the vc->tb_offset_applied for this? We have a reference for the vcore in the hstate already. > #endif > }; > > diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c > index b12d7c049bfe..0beb8fdc6352 100644 > --- a/arch/powerpc/kernel/asm-offsets.c > +++ b/arch/powerpc/kernel/asm-offsets.c > @@ -706,6 +706,7 @@ int main(void) > HSTATE_FIELD(HSTATE_CFAR, cfar); > HSTATE_FIELD(HSTATE_PPR, ppr); > HSTATE_FIELD(HSTATE_HOST_FSCR, host_fscr); > + HSTATE_FIELD(HSTATE_TB_OFFSET, tb_offset); > #endif /* CONFIG_PPC_BOOK3S_64 */ > > #else /* CONFIG_PPC_BOOK3S */ > diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c > index 67feb3524460..f27f0163792b 100644 > --- a/arch/powerpc/kernel/time.c > +++ b/arch/powerpc/kernel/time.c > @@ -699,7 +699,13 @@ EXPORT_SYMBOL_GPL(tb_to_ns); > */ > notrace unsigned long long sched_clock(void) > { > - return mulhdu(get_tb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift; > + u64 tb = get_tb() - boot_tb; > + > +#if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_KVM_BOOK3S_HANDLER) > + tb -= local_paca->kvm_hstate.tb_offset; > +#endif > + > + return mulhdu(tb, tb_to_ns_scale) << tb_to_ns_shift; > } > > > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > index b3731572295e..c08593c63353 100644 > --- a/arch/powerpc/kvm/book3s_hv.c > +++ b/arch/powerpc/kvm/book3s_hv.c > @@ -3491,6 +3491,7 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit, > if ((tb & 0xffffff) < (new_tb & 0xffffff)) > mtspr(SPRN_TBU40, new_tb + 0x1000000); > vc->tb_offset_applied = vc->tb_offset; > + local_paca->kvm_hstate.tb_offset = vc->tb_offset; > } > > if (vc->pcr) > @@ -3594,6 +3595,7 @@ static int kvmhv_load_hv_regs_and_go(struct kvm_vcpu *vcpu, u64 time_limit, > if ((tb & 0xffffff) < (new_tb & 0xffffff)) > mtspr(SPRN_TBU40, new_tb + 0x1000000); > vc->tb_offset_applied = 0; > + local_paca->kvm_hstate.tb_offset = 0; > } > > mtspr(SPRN_HDEC, 0x7fffffff); > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > index b73140607875..8f7a9f7f4ee6 100644 > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > @@ -632,6 +632,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_300) > cmpdi r8,0 > beq 37f > std r8, VCORE_TB_OFFSET_APPL(r5) > + std r8, HSTATE_TB_OFFSET(r13) > mftb r6 /* current host timebase */ > add r8,r8,r6 > mtspr SPRN_TBU40,r8 /* update upper 40 bits */ > @@ -1907,6 +1908,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) > beq 17f > li r0, 0 > std r0, VCORE_TB_OFFSET_APPL(r5) > + std r0, HSTATE_TB_OFFSET(r13) > mftb r6 /* current guest timebase */ > subf r8,r8,r6 > mtspr SPRN_TBU40,r8 /* update upper 40 bits */
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