linux-kernel - Re: [RFC PATCH v1 01/15] x86/msr: Replace __wrmsr() with native

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Message-ID: <a0254e73-bf7c-4876-b64e-b08e96044666@zytor.com>
Date: Mon, 31 Mar 2025 22:53:49 -0700
From: Xin Li <xin@...or.com>
To: "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
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Subject: Re: [RFC PATCH v1 01/15] x86/msr: Replace __wrmsr() with
 native_wrmsrl()

On 3/31/2025 1:32 PM, H. Peter Anvin wrote:
> On March 31, 2025 3:17:30 AM PDT, Ingo Molnar <mingo@...nel.org> wrote:
>>
>> * Xin Li (Intel) <xin@...or.com> wrote:
>>
>>> -	__wrmsr      (MSR_AMD_DBG_EXTN_CFG, val | 3ULL << 3, val >> 32);
>>> +	native_wrmsrl(MSR_AMD_DBG_EXTN_CFG, val | 3ULL << 3);
>>
>> This is an improvement.
>>
>>> -	__wrmsr      (MSR_IA32_PQR_ASSOC, rmid_p, plr->closid);
>>> +	native_wrmsrl(MSR_IA32_PQR_ASSOC, (u64)plr->closid << 32 | rmid_p);
>>
>>> -	__wrmsr      (MSR_IA32_PQR_ASSOC, rmid_p, closid_p);
>>> +	native_wrmsrl(MSR_IA32_PQR_ASSOC, (u64)closid_p << 32 | rmid_p);
>>
>> This is not an improvement.
>>
>> Please provide a native_wrmsrl() API variant where natural [rmid_p, closid_p]
>> high/lo parameters can be used, without the shift-uglification...
>>
>> Thanks,
>>
>> 	Ingo
> 
> Directing this question primarily to Ingo, who is more than anyone else the namespace consistency guardian:
> 
> On the subject of msr function naming ... *msrl() has always been misleading. The -l suffix usually means 32 bits; sometimes it means the C type "long" (which in the kernel is used instead of size_t/uintptr_t, which might end up being "fun" when 128-bit architectures appear some time this century), but for a fixed 64-but type we normally use -q.
> 
> Should we rename the *msrl() functions to *msrq() as part of this overhaul?
> 

Per "struct msr" defined in arch/x86/include/asm/shared/msr.h:

struct msr {
         union {
                 struct {
                         u32 l;
                         u32 h;
                 };
                 u64 q;
         };
};

Probably *msrq() is what we want?