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

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Date:	Tue, 22 Jul 2014 00:30:18 +0300
From:	Nadav Amit <nadav.amit@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	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

Few comments to see we are on the same page:

On 7/21/14, 3:18 PM, Paolo Bonzini wrote:
> Il 21/07/2014 13:37, Nadav Amit ha scritto:
>> +int kvm_exception_type(unsigned int nr)
>
> The manual calls this the exception class.
Yes, but it also calls it exception "type" (see table 6-1 
"Protected-Mode Exceptions and Interrupts" on the SDM).
I called it exception type, since there is a function exception_class 
that is used to handle nested exceptions.

>> +	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.
Unless I am mistaken, kvm_vcpu_check_breakpoint checks only for 
instruction breakpoint. Since instruction breakpoint should not cause RF 
to be set, this function should not be changed.

Anyhow, I would return EXCPT_TRAP on DB_VECTOR.

Nadav

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