From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Jones Subject: Re: [PATCH v2 9/9] KVM: arm/arm64: avoid race by caching MPIDR Date: Wed, 5 Apr 2017 10:50:05 +0200 Message-ID: <20170405085005.waetpjcvgdglmayp@kamzik.brq.redhat.com> References: <20170331160658.4331-1-drjones@redhat.com> <20170331160658.4331-10-drjones@redhat.com> <20170404194439.GI31208@cbox> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: marc.zyngier@arm.com, pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org To: Christoffer Dall Return-path: Content-Disposition: inline In-Reply-To: <20170404194439.GI31208@cbox> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu List-Id: kvm.vger.kernel.org On Tue, Apr 04, 2017 at 09:44:39PM +0200, Christoffer Dall wrote: > On Fri, Mar 31, 2017 at 06:06:58PM +0200, Andrew Jones wrote: > > Cache the MPIDR in the vcpu structure to fix potential races that > > can arise between vcpu reset and the extraction of the MPIDR from > > the sys-reg array. > > I don't understand the race, sorry. > > Can you be more specific in where this goes wrong and exactly what this > fixes? > At the start of kvm_psci_vcpu_on() we look up the vcpu struct of the target vcpu by MPIDR. vcpu = kvm_mpidr_to_vcpu(kvm, cpu_id); This necessarily comes before the newly added if (!test_and_clear_bit(KVM_REQ_POWER_OFF, &vcpu->requests)) If another vcpu is trying to PSCI_ON the same target vcpu at the same time, but is further along, i.e. already past the test-and-clear and even in kvm_reset_vcpu(), then there's a chance it has already called into kvm_reset_sys_regs(), which does /* Catch someone adding a register without putting in reset entry. */ memset(&vcpu->arch.ctxt.sys_regs, 0x42, sizeof(vcpu->arch.ctxt.sys_regs)); but has not yet called reset_mpidr(). In that case the kvm_mpidr_to_vcpu() pointed out above will fail to find the vcpu, which results in the PSCI_ON call returning PSCI_RET_INVALID_PARAMS, as can be seen from this snip of kvm_psci_vcpu_on() static unsigned long kvm_psci_vcpu_on(struct kvm_vcpu *source_vcpu) { struct kvm *kvm = source_vcpu->kvm; struct kvm_vcpu *vcpu = NULL; struct swait_queue_head *wq; unsigned long cpu_id; unsigned long context_id; phys_addr_t target_pc; cpu_id = vcpu_get_reg(source_vcpu, 1) & MPIDR_HWID_BITMASK; if (vcpu_mode_is_32bit(source_vcpu)) cpu_id &= ~((u32) 0); vcpu = kvm_mpidr_to_vcpu(kvm, cpu_id); /* * Make sure the caller requested a valid CPU and that the CPU is * turned off. */ if (!vcpu) return PSCI_RET_INVALID_PARAMS; if (!test_and_clear_bit(KVM_REQ_POWER_OFF, &vcpu->requests)) { ... Thanks, drew > Thanks, > -Christoffer > > > > > Signed-off-by: Andrew Jones > > --- > > arch/arm/include/asm/kvm_emulate.h | 2 +- > > arch/arm/include/asm/kvm_host.h | 3 +++ > > arch/arm/kvm/coproc.c | 20 ++++++++++++-------- > > arch/arm64/include/asm/kvm_emulate.h | 2 +- > > arch/arm64/include/asm/kvm_host.h | 3 +++ > > arch/arm64/kvm/sys_regs.c | 27 ++++++++++++++------------- > > 6 files changed, 34 insertions(+), 23 deletions(-) > > > > diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h > > index 9a8a45aaf19a..1b922de46785 100644 > > --- a/arch/arm/include/asm/kvm_emulate.h > > +++ b/arch/arm/include/asm/kvm_emulate.h > > @@ -213,7 +213,7 @@ static inline u32 kvm_vcpu_hvc_get_imm(struct kvm_vcpu *vcpu) > > > > static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu) > > { > > - return vcpu_cp15(vcpu, c0_MPIDR) & MPIDR_HWID_BITMASK; > > + return vcpu->arch.vmpidr & MPIDR_HWID_BITMASK; > > } > > > > static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu) > > diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h > > index 0b8a6d6b3cb3..e0f461f0af67 100644 > > --- a/arch/arm/include/asm/kvm_host.h > > +++ b/arch/arm/include/asm/kvm_host.h > > @@ -151,6 +151,9 @@ struct kvm_vcpu_arch { > > /* The CPU type we expose to the VM */ > > u32 midr; > > > > + /* vcpu MPIDR */ > > + u32 vmpidr; > > + > > /* HYP trapping configuration */ > > u32 hcr; > > > > diff --git a/arch/arm/kvm/coproc.c b/arch/arm/kvm/coproc.c > > index 3e5e4194ef86..c4df7c9c8ddb 100644 > > --- a/arch/arm/kvm/coproc.c > > +++ b/arch/arm/kvm/coproc.c > > @@ -101,14 +101,18 @@ int kvm_handle_cp14_access(struct kvm_vcpu *vcpu, struct kvm_run *run) > > > > static void reset_mpidr(struct kvm_vcpu *vcpu, const struct coproc_reg *r) > > { > > - /* > > - * Compute guest MPIDR. We build a virtual cluster out of the > > - * vcpu_id, but we read the 'U' bit from the underlying > > - * hardware directly. > > - */ > > - vcpu_cp15(vcpu, c0_MPIDR) = ((read_cpuid_mpidr() & MPIDR_SMP_BITMASK) | > > - ((vcpu->vcpu_id >> 2) << MPIDR_LEVEL_BITS) | > > - (vcpu->vcpu_id & 3)); > > + if (!vcpu->arch.vmpidr) { > > + /* > > + * Compute guest MPIDR. We build a virtual cluster out of the > > + * vcpu_id, but we read the 'U' bit from the underlying > > + * hardware directly. > > + */ > > + u32 mpidr = ((read_cpuid_mpidr() & MPIDR_SMP_BITMASK) | > > + ((vcpu->vcpu_id >> 2) << MPIDR_LEVEL_BITS) | > > + (vcpu->vcpu_id & 3)); > > + vcpu->arch.vmpidr = mpidr; > > + } > > + vcpu_cp15(vcpu, c0_MPIDR) = vcpu->arch.vmpidr; > > } > > > > /* TRM entries A7:4.3.31 A15:4.3.28 - RO WI */ > > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h > > index f5ea0ba70f07..c138bb15b507 100644 > > --- a/arch/arm64/include/asm/kvm_emulate.h > > +++ b/arch/arm64/include/asm/kvm_emulate.h > > @@ -242,7 +242,7 @@ static inline u8 kvm_vcpu_trap_get_fault_type(const struct kvm_vcpu *vcpu) > > > > static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu) > > { > > - return vcpu_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK; > > + return vcpu->arch.vmpidr_el2 & MPIDR_HWID_BITMASK; > > } > > > > static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > > index 7057512b3474..268c10d95a79 100644 > > --- a/arch/arm64/include/asm/kvm_host.h > > +++ b/arch/arm64/include/asm/kvm_host.h > > @@ -198,6 +198,9 @@ typedef struct kvm_cpu_context kvm_cpu_context_t; > > struct kvm_vcpu_arch { > > struct kvm_cpu_context ctxt; > > > > + /* vcpu MPIDR */ > > + u64 vmpidr_el2; > > + > > /* HYP configuration */ > > u64 hcr_el2; > > u32 mdcr_el2; > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > index 0e26f8c2b56f..517aed6d8016 100644 > > --- a/arch/arm64/kvm/sys_regs.c > > +++ b/arch/arm64/kvm/sys_regs.c > > @@ -431,19 +431,20 @@ static void reset_amair_el1(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r) > > > > static void reset_mpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r) > > { > > - u64 mpidr; > > - > > - /* > > - * Map the vcpu_id into the first three affinity level fields of > > - * the MPIDR. We limit the number of VCPUs in level 0 due to a > > - * limitation to 16 CPUs in that level in the ICC_SGIxR registers > > - * of the GICv3 to be able to address each CPU directly when > > - * sending IPIs. > > - */ > > - mpidr = (vcpu->vcpu_id & 0x0f) << MPIDR_LEVEL_SHIFT(0); > > - mpidr |= ((vcpu->vcpu_id >> 4) & 0xff) << MPIDR_LEVEL_SHIFT(1); > > - mpidr |= ((vcpu->vcpu_id >> 12) & 0xff) << MPIDR_LEVEL_SHIFT(2); > > - vcpu_sys_reg(vcpu, MPIDR_EL1) = (1ULL << 31) | mpidr; > > + if (!vcpu->arch.vmpidr_el2) { > > + /* > > + * Map the vcpu_id into the first three affinity level fields > > + * of the MPIDR. We limit the number of VCPUs in level 0 due to > > + * a limitation of 16 CPUs in that level in the ICC_SGIxR > > + * registers of the GICv3, which are used to address each CPU > > + * directly when sending IPIs. > > + */ > > + u64 mpidr = (vcpu->vcpu_id & 0x0f) << MPIDR_LEVEL_SHIFT(0); > > + mpidr |= ((vcpu->vcpu_id >> 4) & 0xff) << MPIDR_LEVEL_SHIFT(1); > > + mpidr |= ((vcpu->vcpu_id >> 12) & 0xff) << MPIDR_LEVEL_SHIFT(2); > > + vcpu->arch.vmpidr_el2 = (1ULL << 31) | mpidr; > > + } > > + vcpu_sys_reg(vcpu, MPIDR_EL1) = vcpu->arch.vmpidr_el2; > > } > > > > static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r) > > -- > > 2.9.3 > >