linux-kernel - Re: [PATCH hyperv-next v2 3/4] arch: hyperv: Get/set SynIC synth.registers via paravisor

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Message-ID: <a7ad48ca-2346-4039-a3a9-f93317b2d1a1@linux.microsoft.com>
Date: Tue, 13 May 2025 09:31:36 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: ALOK TIWARI <alok.a.tiwari@...cle.com>
Cc: apais@...rosoft.com, benhill@...rosoft.com, bperkins@...rosoft.com,
 sunilmut@...rosoft.com, arnd@...db.de, bp@...en8.de,
 catalin.marinas@....com, corbet@....net, dave.hansen@...ux.intel.com,
 decui@...rosoft.com, haiyangz@...rosoft.com, hpa@...or.com,
 kys@...rosoft.com, mingo@...hat.com, tglx@...utronix.de, wei.liu@...nel.org,
 will@...nel.org, x86@...nel.org, linux-hyperv@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH hyperv-next v2 3/4] arch: hyperv: Get/set SynIC
 synth.registers via paravisor



On 5/12/2025 2:39 AM, ALOK TIWARI wrote:
> 
> 
> On 12-05-2025 04:37, Roman Kisel wrote:
>> +/*
>> + * Not every paravisor supports getting SynIC registers, and
>> + * this function may fail. The caller has to make sure that this 
>> function
>> + * runs on the CPU of interest.
>> + */
> 
> Title and Intent: Clearly state the purpose of the function in the first 
> sentence
> /*
>   * Attempt to get the SynIC register value.
>   *
>   * Not all paravisors support reading SynIC registers, so this function
>   * may fail. The caller must ensure that it is executed on the target
>   * CPU.
>   *
>   * Returns: The SynIC register value or ~0ULL on failure.
>   * Sets err to -ENODEV if the provided register is not a valid SynIC
>   * MSR.
>   */
> 
>> +u64 hv_pv_get_synic_register(unsigned int reg, int *err)
>> +{
>> +    if (!hv_is_synic_msr(reg)) {
>> +        *err = -ENODEV;
>> +        return !0ULL;
>> +    }
>> +    return native_read_msr_safe(reg, err);
>> +}
>> +EXPORT_SYMBOL_GPL(hv_pv_get_synic_register);
>> +
>> +/*
>> + * Not every paravisor supports setting SynIC registers, and
>> + * this function may fail. The caller has to make sure that this 
>> function
>> + * runs on the CPU of interest.
>> + */
> 
> ditto.
> 
>> +int hv_pv_set_synic_register(unsigned int reg, u64 val)
>> +{
>> +    if (!hv_is_synic_msr(reg))
>> +        return -ENODEV;
>> +    return wrmsrl_safe(reg, val);
>> +}
>> +EXPORT_SYMBOL_GPL(hv_pv_set_synic_register);
> 

Indeed, I wrote a bit of a novel in the comments which might be
distracting and making it harder to find the point :)

Ought to be more conscious of the reader's perhaps constrained
time budget. I'll restructure that as you suggested!

> Thanks,
> Alok
> 

-- 
Thank you,
Roman