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Commit 1880afd6 authored by James Hogan's avatar James Hogan
Browse files

KVM: MIPS/T&E: Add lockless GVA access helpers 



Add helpers to allow for lockless direct access to the GVA space, by
changing the VCPU mode to READING_SHADOW_PAGE_TABLES for the duration of
the access. This allows asynchronous TLB flush requests in future
patches to safely trigger either a TLB flush before the direct GVA space
access, or a delay until the in-progress lockless direct access is
complete.

The kvm_trap_emul_gva_lockless_begin() and
kvm_trap_emul_gva_lockless_end() helpers take care of guarding the
direct GVA accesses, and kvm_trap_emul_gva_fault() tries to handle a
uaccess fault resulting from a flush having taken place.

Signed-off-by: default avatarJames 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
parent 91737ea2

arch/mips/include/asm/kvm_host.h

+15 −0
Original line number Diff line number Diff line
@@ -243,6 +243,7 @@ enum emulation_result { 
#define TLB_ASID(x)		((x).tlb_hi & KVM_ENTRYHI_ASID)

#define TLB_LO_IDX(x, va)	(((va) >> PAGE_SHIFT) & 1)

#define TLB_IS_VALID(x, va)	((x).tlb_lo[TLB_LO_IDX(x, va)] & ENTRYLO_V)

#define TLB_IS_DIRTY(x, va)	((x).tlb_lo[TLB_LO_IDX(x, va)] & ENTRYLO_D)

#define TLB_HI_VPN2_HIT(x, y)	((TLB_VPN2(x) & ~(x).tlb_mask) ==	\

				 ((y) & VPN2_MASK & ~(x).tlb_mask))

#define TLB_HI_ASID_HIT(x, y)	(TLB_IS_GLOBAL(x) ||			\
@@ -640,6 +641,20 @@ pgd_t *kvm_pgd_alloc(void); 
void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);

void kvm_trap_emul_invalidate_gva(struct kvm_vcpu *vcpu, unsigned long addr,

				  bool user);

void kvm_trap_emul_gva_lockless_begin(struct kvm_vcpu *vcpu);

void kvm_trap_emul_gva_lockless_end(struct kvm_vcpu *vcpu);



enum kvm_mips_fault_result {

	KVM_MIPS_MAPPED = 0,

	KVM_MIPS_GVA,

	KVM_MIPS_GPA,

	KVM_MIPS_TLB,

	KVM_MIPS_TLBINV,

	KVM_MIPS_TLBMOD,

};

enum kvm_mips_fault_result kvm_trap_emul_gva_fault(struct kvm_vcpu *vcpu,

						   unsigned long gva,

						   bool write);



/* Emulation */

int kvm_get_inst(u32 *opc, struct kvm_vcpu *vcpu, u32 *out);

arch/mips/kvm/mmu.c

+51 −0
Original line number Diff line number Diff line
@@ -732,6 +732,57 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) 
	local_irq_restore(flags);

}



/**

 * kvm_trap_emul_gva_fault() - Safely attempt to handle a GVA access fault.

 * @vcpu:	Virtual CPU.

 * @gva:	Guest virtual address to be accessed.

 * @write:	True if write attempted (must be dirtied and made writable).

 *

 * Safely attempt to handle a GVA fault, mapping GVA pages if necessary, and

 * dirtying the page if @write so that guest instructions can be modified.

 *

 * Returns:	KVM_MIPS_MAPPED on success.

 *		KVM_MIPS_GVA if bad guest virtual address.

 *		KVM_MIPS_GPA if bad guest physical address.

 *		KVM_MIPS_TLB if guest TLB not present.

 *		KVM_MIPS_TLBINV if guest TLB present but not valid.

 *		KVM_MIPS_TLBMOD if guest TLB read only.

 */

enum kvm_mips_fault_result kvm_trap_emul_gva_fault(struct kvm_vcpu *vcpu,

						   unsigned long gva,

						   bool write)

{

	struct mips_coproc *cop0 = vcpu->arch.cop0;

	struct kvm_mips_tlb *tlb;

	int index;



	if (KVM_GUEST_KSEGX(gva) == KVM_GUEST_KSEG0) {

		if (kvm_mips_handle_kseg0_tlb_fault(gva, vcpu) < 0)

			return KVM_MIPS_GPA;

	} else if ((KVM_GUEST_KSEGX(gva) < KVM_GUEST_KSEG0) ||

		   KVM_GUEST_KSEGX(gva) == KVM_GUEST_KSEG23) {

		/* Address should be in the guest TLB */

		index = kvm_mips_guest_tlb_lookup(vcpu, (gva & VPN2_MASK) |

			  (kvm_read_c0_guest_entryhi(cop0) & KVM_ENTRYHI_ASID));

		if (index < 0)

			return KVM_MIPS_TLB;

		tlb = &vcpu->arch.guest_tlb[index];



		/* Entry should be valid, and dirty for writes */

		if (!TLB_IS_VALID(*tlb, gva))

			return KVM_MIPS_TLBINV;

		if (write && !TLB_IS_DIRTY(*tlb, gva))

			return KVM_MIPS_TLBMOD;



		if (kvm_mips_handle_mapped_seg_tlb_fault(vcpu, tlb, gva))

			return KVM_MIPS_GPA;

	} else {

		return KVM_MIPS_GVA;

	}



	return KVM_MIPS_MAPPED;

}



int kvm_get_inst(u32 *opc, struct kvm_vcpu *vcpu, u32 *out)

{

	int err;

arch/mips/kvm/trap_emul.c

+65 −0
Original line number Diff line number Diff line
@@ -786,6 +786,71 @@ static void kvm_trap_emul_check_requests(struct kvm_vcpu *vcpu, int cpu, 
	}

}



/**

 * kvm_trap_emul_gva_lockless_begin() - Begin lockless access to GVA space.

 * @vcpu:	VCPU pointer.

 *

 * Call before a GVA space access outside of guest mode, to ensure that

 * asynchronous TLB flush requests are handled or delayed until completion of

 * the GVA access (as indicated by a matching kvm_trap_emul_gva_lockless_end()).

 *

 * Should be called with IRQs already enabled.

 */

void kvm_trap_emul_gva_lockless_begin(struct kvm_vcpu *vcpu)

{

	/* We re-enable IRQs in kvm_trap_emul_gva_lockless_end() */

	WARN_ON_ONCE(irqs_disabled());



	/*

	 * The caller is about to access the GVA space, so we set the mode to

	 * force TLB flush requests to send an IPI, and also disable IRQs to

	 * delay IPI handling until kvm_trap_emul_gva_lockless_end().

	 */

	local_irq_disable();



	/*

	 * Make sure the read of VCPU requests is not reordered ahead of the

	 * write to vcpu->mode, or we could miss a TLB flush request while

	 * the requester sees the VCPU as outside of guest mode and not needing

	 * an IPI.

	 */

	smp_store_mb(vcpu->mode, READING_SHADOW_PAGE_TABLES);



	/*

	 * If a TLB flush has been requested (potentially while

	 * OUTSIDE_GUEST_MODE and assumed immediately effective), perform it

	 * before accessing the GVA space, and be sure to reload the ASID if

	 * necessary as it'll be immediately used.

	 *

	 * TLB flush requests after this check will trigger an IPI due to the

	 * mode change above, which will be delayed due to IRQs disabled.

	 */

	kvm_trap_emul_check_requests(vcpu, smp_processor_id(), true);

}



/**

 * kvm_trap_emul_gva_lockless_end() - End lockless access to GVA space.

 * @vcpu:	VCPU pointer.

 *

 * Called after a GVA space access outside of guest mode. Should have a matching

 * call to kvm_trap_emul_gva_lockless_begin().

 */

void kvm_trap_emul_gva_lockless_end(struct kvm_vcpu *vcpu)

{

	/*

	 * Make sure the write to vcpu->mode is not reordered in front of GVA

	 * accesses, or a TLB flush requester may not think it necessary to send

	 * an IPI.

	 */

	smp_store_release(&vcpu->mode, OUTSIDE_GUEST_MODE);



	/*

	 * Now that the access to GVA space is complete, its safe for pending

	 * TLB flush request IPIs to be handled (which indicates completion).

	 */

	local_irq_enable();

}



static void kvm_trap_emul_vcpu_reenter(struct kvm_run *run,

				       struct kvm_vcpu *vcpu)

{