linux-kernel - Re: [PATCH v6 3/5] hyperv: Enable the hypercall output page for the VTL mode

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Message-ID: <18b86a6d-d743-441f-9494-7d36841be210@linux.microsoft.com>
Date: Wed, 8 Jan 2025 15:27:26 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: Roman Kisel <romank@...ux.microsoft.com>, hpa@...or.com,
 kys@...rosoft.com, bp@...en8.de, dave.hansen@...ux.intel.com,
 decui@...rosoft.com, eahariha@...ux.microsoft.com, haiyangz@...rosoft.com,
 mingo@...hat.com, mhklinux@...look.com, tglx@...utronix.de,
 tiala@...rosoft.com, wei.liu@...nel.org, linux-hyperv@...r.kernel.org,
 linux-kernel@...r.kernel.org, x86@...nel.org
Cc: apais@...rosoft.com, benhill@...rosoft.com, ssengar@...rosoft.com,
 sunilmut@...rosoft.com, vdso@...bites.dev
Subject: Re: [PATCH v6 3/5] hyperv: Enable the hypercall output page for the
 VTL mode

On 1/8/2025 2:21 PM, Roman Kisel wrote:
> Due to the hypercall page not being allocated in the VTL mode,
> the code resorts to using a part of the input page.
> 
> Allocate the hypercall output page in the VTL mode thus enabling
> it to use it for output and share code with dom0.
> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> ---
>  drivers/hv/hv_common.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index c6ed3ba4bf61..af5d1dc451f6 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -278,6 +278,11 @@ static void hv_kmsg_dump_register(void)
>  	}
>  }
>  
> +static inline bool hv_output_page_exists(void)
> +{
> +	return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
> +}
> +
>  int __init hv_common_init(void)
>  {
>  	int i;
> @@ -340,7 +345,7 @@ int __init hv_common_init(void)
>  	BUG_ON(!hyperv_pcpu_input_arg);
>  
>  	/* Allocate the per-CPU state for output arg for root */
> -	if (hv_root_partition) {
> +	if (hv_output_page_exists()) {
>  		hyperv_pcpu_output_arg = alloc_percpu(void *);
>  		BUG_ON(!hyperv_pcpu_output_arg);
>  	}
> @@ -435,7 +440,7 @@ int hv_common_cpu_init(unsigned int cpu)
>  	void **inputarg, **outputarg;
>  	u64 msr_vp_index;
>  	gfp_t flags;
> -	int pgcount = hv_root_partition ? 2 : 1;
> +	const int pgcount = hv_output_page_exists() ? 2 : 1;
>  	void *mem;
>  	int ret;
>  
> @@ -453,7 +458,7 @@ int hv_common_cpu_init(unsigned int cpu)
>  		if (!mem)
>  			return -ENOMEM;
>  
> -		if (hv_root_partition) {
> +		if (hv_output_page_exists()) {
>  			outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
>  			*outputarg = (char *)mem + HV_HYP_PAGE_SIZE;
>  		}

Reviewed-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>