Re: [BACKPORT PATCH 3.10..3.16] KVM: MIPS: Drop other CPU ASIDs on guest MMU changes

[Ben Hutchings <ben@decadent.org.uk>]

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On Wed, 2016-11-09 at 14:46 +0000, James Hogan wrote:
> commit 91e4f1b6073dd680d86cdb7e42d7cccca9db39d8 upstream.
> 
> When a guest TLB entry is replaced by TLBWI or TLBWR, we only invalidate
> TLB entries on the local CPU. This doesn't work correctly on an SMP host
> when the guest is migrated to a different physical CPU, as it could pick
> up stale TLB mappings from the last time the vCPU ran on that physical
> CPU.
> 
> Therefore invalidate both user and kernel host ASIDs on other CPUs,
> which will cause new ASIDs to be generated when it next runs on those
> CPUs.
> 
> We're careful only to do this if the TLB entry was already valid, and
> only for the kernel ASID where the virtual address it mapped is outside
> of the guest user address range.
> 
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: linux-mips@linux-mips.org
> Cc: kvm@vger.kernel.org
> Cc: <stable@vger.kernel.org> # 3.10.x-
> Cc: Jiri Slaby <jslaby@suse.cz>
> [james.hogan@imgtec.com: Backport to 3.10..3.16]
> Signed-off-by: James Hogan <james.hogan@imgtec.com>

Queued up for 3.16, thanks.

Ben.

> ---
> Unfortunately the original commit went in to v3.12.65 as commit
> 168e5ebbd63e, without fixing up the references to tlb_lo[0/1] to
> tlb_lo0/1 which broke the MIPS KVM build, and I didn't twig that I
> already had a correct backport outstanding (sorry!). That commit should
> be reverted before applying this backport to 3.12.
> ---
>  arch/mips/kvm/kvm_mips_emul.c | 61 +++++++++++++++++++++++++++++++++++++------
>  1 file changed, 53 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
> index 1983678883c9..d0eb34279955 100644
> --- a/arch/mips/kvm/kvm_mips_emul.c
> +++ b/arch/mips/kvm/kvm_mips_emul.c
> @@ -817,6 +817,47 @@ enum emulation_result kvm_mips_emul_tlbr(struct kvm_vcpu *vcpu)
> >  	return er;
>  }
>  
> +/**
> + * kvm_mips_invalidate_guest_tlb() - Indicates a change in guest MMU map.
> > + * @vcpu:	VCPU with changed mappings.
> > + * @tlb:	TLB entry being removed.
> + *
> + * This is called to indicate a single change in guest MMU mappings, so that we
> + * can arrange TLB flushes on this and other CPUs.
> + */
> +static void kvm_mips_invalidate_guest_tlb(struct kvm_vcpu *vcpu,
> > +					  struct kvm_mips_tlb *tlb)
> +{
> > +	int cpu, i;
> > +	bool user;
> +
> > +	/* No need to flush for entries which are already invalid */
> > +	if (!((tlb->tlb_lo0 | tlb->tlb_lo1) & MIPS3_PG_V))
> > +		return;
> > +	/* User address space doesn't need flushing for KSeg2/3 changes */
> > +	user = tlb->tlb_hi < KVM_GUEST_KSEG0;
> +
> > +	preempt_disable();
> +
> > +	/*
> > +	 * Probe the shadow host TLB for the entry being overwritten, if one
> > +	 * matches, invalidate it
> > +	 */
> > +	kvm_mips_host_tlb_inv(vcpu, tlb->tlb_hi);
> +
> > +	/* Invalidate the whole ASID on other CPUs */
> > +	cpu = smp_processor_id();
> > +	for_each_possible_cpu(i) {
> > +		if (i == cpu)
> > +			continue;
> > +		if (user)
> > +			vcpu->arch.guest_user_asid[i] = 0;
> > +		vcpu->arch.guest_kernel_asid[i] = 0;
> > +	}
> +
> > +	preempt_enable();
> +}
> +
>  /* Write Guest TLB Entry @ Index */
>  enum emulation_result kvm_mips_emul_tlbwi(struct kvm_vcpu *vcpu)
>  {
> @@ -838,10 +879,8 @@ enum emulation_result kvm_mips_emul_tlbwi(struct kvm_vcpu *vcpu)
> >  	}
>  
> >  	tlb = &vcpu->arch.guest_tlb[index];
> -#if 1
> > -	/* Probe the shadow host TLB for the entry being overwritten, if one matches, invalidate it */
> > -	kvm_mips_host_tlb_inv(vcpu, tlb->tlb_hi);
> -#endif
> +
> > +	kvm_mips_invalidate_guest_tlb(vcpu, tlb);
>  
> >  	tlb->tlb_mask = kvm_read_c0_guest_pagemask(cop0);
> >  	tlb->tlb_hi = kvm_read_c0_guest_entryhi(cop0);
> @@ -880,10 +919,7 @@ enum emulation_result kvm_mips_emul_tlbwr(struct kvm_vcpu *vcpu)
>  
> >  	tlb = &vcpu->arch.guest_tlb[index];
>  
> -#if 1
> > -	/* Probe the shadow host TLB for the entry being overwritten, if one matches, invalidate it */
> > -	kvm_mips_host_tlb_inv(vcpu, tlb->tlb_hi);
> -#endif
> > +	kvm_mips_invalidate_guest_tlb(vcpu, tlb);
>  
> >  	tlb->tlb_mask = kvm_read_c0_guest_pagemask(cop0);
> >  	tlb->tlb_hi = kvm_read_c0_guest_entryhi(cop0);
> @@ -926,6 +962,7 @@ kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, uint32_t cause,
> >  	int32_t rt, rd, copz, sel, co_bit, op;
> >  	uint32_t pc = vcpu->arch.pc;
> >  	unsigned long curr_pc;
> > +	int cpu, i;
>  
> >  	/*
> >  	 * Update PC and hold onto current PC in case there is
> @@ -1037,8 +1074,16 @@ kvm_mips_emulate_CP0(uint32_t inst, uint32_t *opc, uint32_t cause,
> >  					     ASID_MASK,
> >  					     vcpu->arch.gprs[rt] & ASID_MASK);
>  
> > +					preempt_disable();
> >  					/* Blow away the shadow host TLBs */
> >  					kvm_mips_flush_host_tlb(1);
> > +					cpu = smp_processor_id();
> > +					for_each_possible_cpu(i)
> > +						if (i != cpu) {
> > +							vcpu->arch.guest_user_asid[i] = 0;
> > +							vcpu->arch.guest_kernel_asid[i] = 0;
> > +						}
> > +					preempt_enable();
> >  				}
> >  				kvm_write_c0_guest_entryhi(cop0,
>  							   vcpu->arch.gprs[rt]);
-- 
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.


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