linux-kernel - Re: [PATCH v3 3/7] Drivers: hv: Provide arch-neutral implementation of get

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Message-ID: <Zq2GMNnRFqH4psLv@liuwe-devbox-debian-v2>
Date: Sat, 3 Aug 2024 01:21:52 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: arnd@...db.de, bhelgaas@...gle.com, bp@...en8.de,
	catalin.marinas@....com, dave.hansen@...ux.intel.com,
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	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
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	ssengar@...ux.microsoft.com
Subject: Re: [PATCH v3 3/7] Drivers: hv: Provide arch-neutral implementation
 of get_vtl()

On Fri, Jul 26, 2024 at 03:59:06PM -0700, Roman Kisel wrote:
> To run in the VTL mode, Hyper-V drivers have to know what
> VTL the system boots in, and the arm64/hyperv code does not
> have the means to compute that.
> 
> Refactor the code to hoist the function that detects VTL,
> make it arch-neutral to be able to employ it to get the VTL
> on arm64. Fix the hypercall output address in `get_vtl(void)`
> not to overlap with the hypercall input area to adhere to
> the Hyper-V TLFS.

Can you split the fix out? That potentially can be backported.

> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
> ---
> +
> +#if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
> +u8 __init get_vtl(void)
> +{
> +	u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS;
> +	struct hv_get_vp_registers_input *input;
> +	struct hv_get_vp_registers_output *output;
> +	unsigned long flags;
> +	u64 ret;
> +
> +	local_irq_save(flags);
> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
> +	output = *this_cpu_ptr(hyperv_pcpu_output_arg);

Hmm... I don't remember why the old code didn't use
hyperv_pcpu_output_arg but instead reused input+OFFSET as output.

Saurabh, can you comment on this?

Thanks,
Wei.