From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jan Kiszka <jan.kiszka@web.de>
Subject: Re: [kvm-devel] [RFC][PATCH 2/4] kvm: Arch-specifc KVM_EXIT_DEBUG
 payload
Date: Thu, 22 May 2008 15:42:07 +0200
Message-ID: <4835782F.60804@web.de>
References: <482D9198.7040801@web.de> <482DAFF6.3050403@web.de> <48344820.60103@qumranet.com>
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Cc: kvm-devel <kvm@vger.kernel.org>,
	Hollis Blanchard <hollisb@us.ibm.com>
To: Avi Kivity <avi@qumranet.com>
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Avi Kivity wrote:
> Jan Kiszka wrote:
>> This adds an arch field to kvm_run.debug, the payload that is returned=

>> to user space on KVM_EXIT_DEBUG guest exits. For x86, this field is no=
w
>> supposed to report the precise debug exception (#DB or #BP) and the
>> current state of the debug registers (the latter is not yet
>> implemented).
>> =20
>> +struct kvm_debug_exit_arch {
>> +    __u32 exception;
>>  =20
>=20
> Need padding here.
>=20
>> +    __u64 dr[8];
>> +};
>> +
>>  =20
>=20
> In general I prefer decoding bitfields into something more usable (see
> for example the segment registers), but in this case, I guess the raw
> registers are better.

IMHO, there is no point in parsing those arch-specific bit field in
kernel space as long as the kernel has nothing to do with them (except
saving and restoring them).

BTW, the upcoming version will look like this:

struct kvm_debug_exit_arch {
        __u32 exception;
        __u32 pad;
        __u64 dr6;
        __u64 dr7;
};

(No need for reporting unused or unmodified registers here.)

>=20
> We need to handle branch tracing and last branch recording as well.  It=

> doesn't have to be in this patchset, though.

IIRC, both features are fairly vendor specific. Do we have the same
level of support on both AMD and Intel CPUs? Moreover, I doubt that the
debug interface would be the right place for them.

Jan


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