linux-kernel - Re: [PATCH v1 1/3] x86/traps: Move DR7_RESET

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Message-ID: <06d93a19-ebc1-418b-becd-225caac76baf@zytor.com>
Date: Fri, 13 Jun 2025 14:38:35 -0700
From: Xin Li <xin@...or.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, pbonzini@...hat.com,
        peterz@...radead.org, brgerst@...il.com, tony.luck@...el.com,
        fenghuay@...dia.com
Subject: Re: [PATCH v1 1/3] x86/traps: Move DR7_RESET_VALUE to
 <uapi/asm/debugreg.h>

On 6/13/2025 1:03 PM, Sean Christopherson wrote:
> On Fri, Jun 13, 2025, Xin Li wrote:
>> On 6/13/2025 7:18 AM, Sean Christopherson wrote:
>>> On Fri, Jun 13, 2025, Xin Li (Intel) wrote:
>>>> Move DR7_RESET_VALUE to <uapi/asm/debugreg.h> to prepare to write DR7
>>>> with DR7_RESET_VALUE at boot time.
>>>
>>> Alternatively, what about dropping DR7_RESET_VALUE,  moving KVM's DR6 and DR7
>>> #defines out of arch/x86/include/asm/kvm_host.h, and then using DR7_FIXED_1?
>>
>> We definitely should do it, I see quite a few architectural definitions
>> are in KVM only headers (the native FRED patches needed to reuse the event
>> types that were previously VMX-specific and moved them out of KVM
>> headers).
>>
>> Because there is an UAPI header, we probably don't want to remove
>> definitions from it?
> 
> What #defines are in which uapi header?

arch/x86/include/uapi/asm/debugreg.h has:

#define DR_BUS_LOCK     (0x800)         /* bus_lock */
#define DR_STEP         (0x4000)        /* single-step */
#define DR_SWITCH       (0x8000)        /* task switch */

And arch/x86/include/asm/kvm_host.h also has:

#define DR6_BUS_LOCK   (1 << 11)
#define DR6_BD          (1 << 13)
#define DR6_BS          (1 << 14)
#define DR6_BT          (1 << 15)
#define DR6_RTM         (1 << 16)

Duplicated definitions for the same DR6 bits.