Re: [PATCH 3/7] KVM: PPC: debug stub interface parameter defined

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2013-03-14 12:54, Alexander Graf wrote:
> 
> On 14.03.2013, at 05:42, Bhushan Bharat-R65777 wrote:
> 
>>
>>
>>> -----Original Message-----
>>> From: Alexander Graf [mailto:agraf@suse.de]
>>> Sent: Thursday, March 07, 2013 6:51 PM
>>> To: Bhushan Bharat-R65777
>>> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org; Wood Scott-B07421; Bhushan
>>> Bharat-R65777
>>> Subject: Re: [PATCH 3/7] KVM: PPC: debug stub interface parameter defined
>>>
>>>
>>> On 28.02.2013, at 05:13, Bharat Bhushan wrote:
>>>
>>>> This patch defines the interface parameter for KVM_SET_GUEST_DEBUG
>>>> ioctl support. Follow up patches will use this for setting up hardware
>>>> breakpoints, watchpoints and software breakpoints.
>>>>
>>>> Also kvm_arch_vcpu_ioctl_set_guest_debug() is brought one level below.
>>>> This is because I am not sure what is required for book3s. So this
>>>> ioctl behaviour will not change for book3s.
>>>>
>>>> Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
>>>> ---
>>>> arch/powerpc/include/uapi/asm/kvm.h |   23 +++++++++++++++++++++++
>>>> arch/powerpc/kvm/book3s.c           |    6 ++++++
>>>> arch/powerpc/kvm/booke.c            |    6 ++++++
>>>> arch/powerpc/kvm/powerpc.c          |    6 ------
>>>> 4 files changed, 35 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/arch/powerpc/include/uapi/asm/kvm.h
>>>> b/arch/powerpc/include/uapi/asm/kvm.h
>>>> index c2ff99c..15f9a00 100644
>>>> --- a/arch/powerpc/include/uapi/asm/kvm.h
>>>> +++ b/arch/powerpc/include/uapi/asm/kvm.h
>>>> @@ -272,8 +272,31 @@ struct kvm_debug_exit_arch {
>>>>
>>>> /* for KVM_SET_GUEST_DEBUG */
>>>> struct kvm_guest_debug_arch {
>>>> +	struct {
>>>> +		/* H/W breakpoint/watchpoint address */
>>>> +		__u64 addr;
>>>> +		/*
>>>> +		 * Type denotes h/w breakpoint, read watchpoint, write
>>>> +		 * watchpoint or watchpoint (both read and write).
>>>> +		 */
>>>> +#define KVMPPC_DEBUG_NOTYPE		0x0
>>>> +#define KVMPPC_DEBUG_BREAKPOINT		(1UL << 1)
>>>> +#define KVMPPC_DEBUG_WATCH_WRITE	(1UL << 2)
>>>> +#define KVMPPC_DEBUG_WATCH_READ		(1UL << 3)
>>>> +		__u32 type;
>>>> +		__u32 reserved;
>>>> +	} bp[16];
>>>> };
>>>>
>>>> +/* Debug related defines */
>>>> +/*
>>>> + * kvm_guest_debug->control is a 32 bit field. The lower 16 bits are
>>>> +generic
>>>> + * and upper 16 bits are architecture specific. Architecture specific
>>>> +defines
>>>> + * that ioctl is for setting hardware breakpoint or software breakpoint.
>>>> + */
>>>> +#define KVM_GUESTDBG_USE_SW_BP		0x00010000
>>>> +#define KVM_GUESTDBG_USE_HW_BP		0x00020000
>>>
>>> You only need
>>>
>>> #define KVM_GUESTDBG_HW_BP 0x00010000
>>>
>>> In absence of the flag, it's a SW breakpoint.
>>
>> We kept this for 2 reasons; 1) Same logic is applied for i386, so trying to keep consistent 2) better clarity.
> 
> Jan, was there any special reason to have 2 flags for HW/SW breakpoint on x86 rather than one bit that indicates which one is used?

Different mechanics on x86: HW goes via debug registers and shows up as
INT1, SW is INT3 (plus guest patching done by user land).

Jan

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