linux-kernel - Re: [PATCH] drivers/xen/xenbus: remove quirk for Xen 3.x

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Message-ID: <alpine.DEB.2.22.394.2508151227420.10166@ubuntu-linux-20-04-desktop>
Date: Fri, 15 Aug 2025 12:27:51 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Juergen Gross <jgross@...e.com>
cc: linux-kernel@...r.kernel.org, Stefano Stabellini <sstabellini@...nel.org>, 
    Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>, 
    xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] drivers/xen/xenbus: remove quirk for Xen 3.x

On Fri, 15 Aug 2025, Juergen Gross wrote:
> The kernel is not supported to run as a Xen guest on Xen versions
> older than 4.0.
> 
> Remove xen_strict_xenbus_quirk() which is testing the Xen version to be
> at least 4.0.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>

Acked-by: Stefano Stabellini <sstabellini@...nel.org>


> ---
>  drivers/xen/xenbus/xenbus_xs.c | 23 -----------------------
>  1 file changed, 23 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
> index 3c9da446b85d..528682bf0c7f 100644
> --- a/drivers/xen/xenbus/xenbus_xs.c
> +++ b/drivers/xen/xenbus/xenbus_xs.c
> @@ -718,26 +718,6 @@ int xs_watch_msg(struct xs_watch_event *event)
>  	return 0;
>  }
>  
> -/*
> - * Certain older XenBus toolstack cannot handle reading values that are
> - * not populated. Some Xen 3.4 installation are incapable of doing this
> - * so if we are running on anything older than 4 do not attempt to read
> - * control/platform-feature-xs_reset_watches.
> - */
> -static bool xen_strict_xenbus_quirk(void)
> -{
> -#ifdef CONFIG_X86
> -	uint32_t eax, ebx, ecx, edx, base;
> -
> -	base = xen_cpuid_base();
> -	cpuid(base + 1, &eax, &ebx, &ecx, &edx);
> -
> -	if ((eax >> 16) < 4)
> -		return true;
> -#endif
> -	return false;
> -
> -}
>  static void xs_reset_watches(void)
>  {
>  	int err;
> @@ -745,9 +725,6 @@ static void xs_reset_watches(void)
>  	if (!xen_hvm_domain() || xen_initial_domain())
>  		return;
>  
> -	if (xen_strict_xenbus_quirk())
> -		return;
> -
>  	if (!xenbus_read_unsigned("control",
>  				  "platform-feature-xs_reset_watches", 0))
>  		return;
> -- 
> 2.43.0
>