linux-kernel - Re: [PATCH 2/7] KVM: x86: Function for determining exception type

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Date:	Mon, 21 Jul 2014 14:18:28 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Nadav Amit <namit@...technion.ac.il>
CC:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, gleb@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] KVM: x86: Function for determining exception type

Il 21/07/2014 13:37, Nadav Amit ha scritto:
> +int kvm_exception_type(unsigned int nr)

The manual calls this the exception class.

Please open code this as an if like this

	int mask;

	/* This should never happen, right? */
	if (WARN_ON(nr > 31))
		return EXCPT_INTERRUPT;

	mask = 1 << nr;
	if (mask &
	    ((1 << DB_VECTOR) | (1 << BP_VECTOR) |
	     (1 << OF_VECTOR)))
		return EXCPT_TRAP;

	...

	/*
	 * If it is reserved, assume it is a fault and
	 * set RF.
	 */
	return EXCPT_FAULT;

> +	case VE_VECTOR:
> +		return EXCPT_FAULT;
> +	case DB_VECTOR:
> +		return EXCPT_FAULT_OR_TRAP;

It is only a fault for instruction fetch breakpoints.  You can modify
kvm_vcpu_check_breakpoint to set RF, add a comment here that fault
handling is done elsewhere, and return EXCPT_TRAP.

Paolo
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