linux-kernel - Re: [PATCH hyperv-next v3 03/15] arch: hyperv: Get/set SynIC synth.registers via paravisor

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Message-ID: <9c5c6a6b-421b-4f26-b3a2-1e10bc3badd1@oracle.com>
Date: Wed, 4 Jun 2025 18:57:01 +0530
From: ALOK TIWARI <alok.a.tiwari@...cle.com>
To: Roman Kisel <romank@...ux.microsoft.com>, arnd@...db.de, bp@...en8.de,
        corbet@....net, dave.hansen@...ux.intel.com, decui@...rosoft.com,
        haiyangz@...rosoft.com, hpa@...or.com, kys@...rosoft.com,
        mingo@...hat.com, mhklinux@...look.com, tglx@...utronix.de,
        wei.liu@...nel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc: apais@...rosoft.com, benhill@...rosoft.com, bperkins@...rosoft.com,
        sunilmut@...rosoft.com
Subject: Re: [PATCH hyperv-next v3 03/15] arch: hyperv: Get/set SynIC
 synth.registers via paravisor



On 04-06-2025 06:13, Roman Kisel wrote:
> The confidential VMBus is built on the guest talking to the
> paravisor only.
> 
> Provide functions that allow manipulating the SynIC registers
> via paravisor. No functional changes.
> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> Reviewed-by: Alok Tiwari <alok.a.tiwari@...cle.com>
> ---
>   arch/x86/kernel/cpu/mshyperv.c | 44 ++++++++++++++++++++++++++++++++++
>   drivers/hv/hv_common.c         | 13 ++++++++++
>   include/asm-generic/mshyperv.h |  2 ++
>   3 files changed, 59 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 3e2533954675..83a85d94bcb3 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -89,6 +89,50 @@ void hv_set_non_nested_msr(unsigned int reg, u64 value)
>   }
>   EXPORT_SYMBOL_GPL(hv_set_non_nested_msr);
>   
> +/*
> + * Attempt to get the SynIC register value from the paravisor.
> + *
> + * Not all paravisors support reading SynIC registers, so this function
> + * may fail. The register for the SynIC of the running CPU is accessed.
> + *
> + * Writes the SynIC register value into the memory pointed by val,
> + * and ~0ULL is on failure.
> + *
> + * Returns -ENODEV if the MSR is not a SynIC register, or another error
> + * code if getting the MSR fails (meaning the paravisor doesn't support
> + * relaying VMBus comminucations).

comminucations -> communications

> + */
> +int hv_para_get_synic_register(unsigned int reg, u64 *val)
> +{
> +	u64 reg_val = ~0ULL;
> +	int err = -ENODEV;
> +
> +	if (hv_is_synic_msr(reg))
> +		reg_val = native_read_msr_safe(reg, &err);
> +	*val = reg_val;
> +
> +	return err;
> +}
> +
> +/*
> + * Attempt to set the SynIC register value with the paravisor.
> + *
> + * Not all paravisors support reading SynIC registers, so this function
> + * may fail. The register for the SynIC of the running CPU is accessed.

you are writing, not reading. ?
-> "Not all paravisors support writing SynIC registers"

> + *
> + * Sets the register to the value supplied.
> + *
> + * Returns: -ENODEV if the MSR is not a SynIC register, or another error
> + * code if writing to the MSR fails (meaning the paravisor doesn't support
> + * relaying VMBus comminucations).
> + */
> +int hv_para_set_synic_register(unsigned int reg, u64 val)
> +{
> +	if (!hv_is_synic_msr(reg))
> +		return -ENODEV;
> +	return wrmsrl_safe(reg, val);
> +}


Thanks,
Alok