On Wed, Apr 05, 2017 at 10:50:05AM +0200, Andrew Jones wrote:
> 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));
Ah right, I didn't remember that we did this.
>
> 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 for the explanation. Could you add this to the commit message as
you respin:
...arise between vcpu reset, which fills the entire sys_regs array
with a temporary value including the MPIDR register, and looking up
the VCPU based on the MPIDR value.
With that:
Reviewed-by: Christoffer Dall <cdall@xxxxxxxxxx>
>
> > Thanks,
> > -Christoffer
> >
> > >
> > > Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
> > > ---
> > > 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
> > >
