linux-kernel - Re: [PATCH] x86/hyperv: add noop functions to x86

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Date:   Fri, 2 Jun 2023 16:22:44 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Saurabh Sengar <ssengar@...ux.microsoft.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        mikelley@...rosoft.com, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, hpa@...or.com
Subject: Re: [PATCH] x86/hyperv: add noop functions to x86_init mpparse
 functions

On Fri, Jun 02, 2023 at 05:41:52AM -0700, Saurabh Sengar wrote:
> In !ACPI system, there is no way to disable CONFIG_X86_MPPARSE.
> When CONFIG_X86_MPPARSE is enabled for VTL2, the kernel will
> scan low memory looking for MP tables. Don't allow this, because
> low memory is controlled by VTL0 and may contain actual valid
> tables for VTL0, which can confuse the VTL2 kernel.
> 
> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_vtl.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 1ba5d3b99b16..ea21d897b5da 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -23,6 +23,10 @@ void __init hv_vtl_init_platform(void)
>  	x86_init.irqs.pre_vector_init = x86_init_noop;
>  	x86_init.timers.timer_init = x86_init_noop;
>  
> +	/* Avoid searching for BIOS MP tables */
> +	x86_init.mpparse.find_smp_config = x86_init_noop;
> +	x86_init.mpparse.get_smp_config = x86_init_uint_noop;
> +

The code looks fine.

Can you expand the commit message a bit so that people who are not
familiar with VTL and your setup can understand what's going on?

Thanks,
Wei.

>  	x86_platform.get_wallclock = get_rtc_noop;
>  	x86_platform.set_wallclock = set_rtc_noop;
>  	x86_platform.get_nmi_reason = hv_get_nmi_reason;
> -- 
> 2.34.1
>