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Commit 6a97c775 authored by James Hogan's avatar James Hogan
Browse files

KVM: MIPS: Use CP0_BadInstr[P] for emulation 



When exiting from the guest, store the values of the CP0_BadInstr and
CP0_BadInstrP registers if they exist, which contain the encodings of
the instructions which caused the last synchronous exception.

When the instruction is needed for emulation, kvm_get_badinstr() and
kvm_get_badinstrp() are used instead of calling kvm_get_inst() directly,
to decide whether to read the saved CP0_BadInstr/CP0_BadInstrP registers
(if they exist), or read the instruction from memory (if not).

The use of these registers should be more robust than using
kvm_get_inst(), as it actually gives the instruction encoding seen by
the hardware rather than relying on user accessors after the fact, which
can be fooled by incoherent icache or a racing code modification. It
will also work with VZ, where the guest virtual memory isn't directly
accessible by the host with user accessors.

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 122e51d4

arch/mips/include/asm/kvm_host.h

+4 −0
Original line number Diff line number Diff line
@@ -280,6 +280,8 @@ struct kvm_vcpu_arch { 
	unsigned long host_cp0_badvaddr;

	unsigned long host_cp0_epc;

	u32 host_cp0_cause;

	u32 host_cp0_badinstr;

	u32 host_cp0_badinstrp;



	/* GPRS */

	unsigned long gprs[32];
@@ -641,6 +643,8 @@ void kvm_trap_emul_invalidate_gva(struct kvm_vcpu *vcpu, unsigned long addr, 
/* Emulation */

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

enum emulation_result update_pc(struct kvm_vcpu *vcpu, u32 cause);

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

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



/**

 * kvm_is_ifetch_fault() - Find whether a TLBL exception is due to ifetch fault.

arch/mips/kvm/emulate.c

+45 −3
Original line number Diff line number Diff line
@@ -54,7 +54,7 @@ static int kvm_compute_return_epc(struct kvm_vcpu *vcpu, unsigned long instpc, 
	}



	/* Read the instruction */

	err = kvm_get_inst((u32 *)epc, vcpu, &insn.word);

	err = kvm_get_badinstrp((u32 *)epc, vcpu, &insn.word);

	if (err)

		return err;
@@ -258,6 +258,48 @@ enum emulation_result update_pc(struct kvm_vcpu *vcpu, u32 cause) 
	return EMULATE_DONE;

}



/**

 * kvm_get_badinstr() - Get bad instruction encoding.

 * @opc:	Guest pointer to faulting instruction.

 * @vcpu:	KVM VCPU information.

 *

 * Gets the instruction encoding of the faulting instruction, using the saved

 * BadInstr register value if it exists, otherwise falling back to reading guest

 * memory at @opc.

 *

 * Returns:	The instruction encoding of the faulting instruction.

 */

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

{

	if (cpu_has_badinstr) {

		*out = vcpu->arch.host_cp0_badinstr;

		return 0;

	} else {

		return kvm_get_inst(opc, vcpu, out);

	}

}



/**

 * kvm_get_badinstrp() - Get bad prior instruction encoding.

 * @opc:	Guest pointer to prior faulting instruction.

 * @vcpu:	KVM VCPU information.

 *

 * Gets the instruction encoding of the prior faulting instruction (the branch

 * containing the delay slot which faulted), using the saved BadInstrP register

 * value if it exists, otherwise falling back to reading guest memory at @opc.

 *

 * Returns:	The instruction encoding of the prior faulting instruction.

 */

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

{

	if (cpu_has_badinstrp) {

		*out = vcpu->arch.host_cp0_badinstrp;

		return 0;

	} else {

		return kvm_get_inst(opc, vcpu, out);

	}

}



/**

 * kvm_mips_count_disabled() - Find whether the CP0_Count timer is disabled.

 * @vcpu:	Virtual CPU.
@@ -1839,7 +1881,7 @@ enum emulation_result kvm_mips_emulate_inst(u32 cause, u32 *opc, 
	/* Fetch the instruction. */

	if (cause & CAUSEF_BD)

		opc += 1;

	err = kvm_get_inst(opc, vcpu, &inst.word);

	err = kvm_get_badinstr(opc, vcpu, &inst.word);

	if (err)

		return EMULATE_FAIL;
@@ -2434,7 +2476,7 @@ enum emulation_result kvm_mips_handle_ri(u32 cause, u32 *opc, 
	/* Fetch the instruction. */

	if (cause & CAUSEF_BD)

		opc += 1;

	err = kvm_get_inst(opc, vcpu, &inst.word);

	err = kvm_get_badinstr(opc, vcpu, &inst.word);

	if (err) {

		kvm_err("%s: Cannot get inst @ %p (%d)\n", __func__, opc, err);

		return EMULATE_FAIL;

arch/mips/kvm/entry.c

+14 −0
Original line number Diff line number Diff line
@@ -53,6 +53,8 @@ 
/* Some CP0 registers */

#define C0_HWRENA	7, 0

#define C0_BADVADDR	8, 0

#define C0_BADINSTR	8, 1

#define C0_BADINSTRP	8, 2

#define C0_ENTRYHI	10, 0

#define C0_STATUS	12, 0

#define C0_CAUSE	13, 0
@@ -579,6 +581,18 @@ void *kvm_mips_build_exit(void *addr) 
	uasm_i_mfc0(&p, K0, C0_CAUSE);

	uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch, host_cp0_cause), K1);



	if (cpu_has_badinstr) {

		uasm_i_mfc0(&p, K0, C0_BADINSTR);

		uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch,

					   host_cp0_badinstr), K1);

	}



	if (cpu_has_badinstrp) {

		uasm_i_mfc0(&p, K0, C0_BADINSTRP);

		uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch,

					   host_cp0_badinstrp), K1);

	}



	/* Now restore the host state just enough to run the handlers */



	/* Switch EBASE to the one used by Linux */

arch/mips/kvm/mips.c

+1 −1
Original line number Diff line number Diff line
@@ -1471,7 +1471,7 @@ int kvm_mips_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu) 
		if (cause & CAUSEF_BD)

			opc += 1;

		inst = 0;

		kvm_get_inst(opc, vcpu, &inst);

		kvm_get_badinstr(opc, vcpu, &inst);

		kvm_err("Exception Code: %d, not yet handled, @ PC: %p, inst: 0x%08x  BadVaddr: %#lx Status: %#lx\n",

			exccode, opc, inst, badvaddr,

			kvm_read_c0_guest_status(vcpu->arch.cop0));