linux-kernel - Re: [PATCH 5/5] x86/Hyper-V: Add Hyper-V specific hvcall to set backing page

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Message-ID: <20250918150959.GEaMwgx78CGCxjGce8@fat_crate.local>
Date: Thu, 18 Sep 2025 17:09:59 +0200
From: Borislav Petkov <bp@...en8.de>
To: Tianyu Lan <ltykernel@...il.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
	arnd@...db.de, Neeraj.Upadhyay@....com, tiala@...rosoft.com,
	kvijayab@....com, romank@...ux.microsoft.com,
	linux-arch@...r.kernel.org, linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] x86/Hyper-V: Add Hyper-V specific hvcall to set
 backing page

On Thu, Sep 18, 2025 at 11:00:23AM -0400, Tianyu Lan wrote:
> Secure AVIC hardware provides APIC backing page
> to aid the guest in limiting which interrupt
> vectors can be injected into the guest. Hyper-V
> introduces a new register HV_X64_REGISTER_SEV_GPA_PAGE
> to notify hypervisor with APIC backing page and call
> it in Secure AVIC driver.

Why does hyperv needs special handling again and cannot simply adhere to the
secure AVIC spec?

None of that text explains *why* it is absolutely necessary to do something
hyperv-special...

> @@ -361,7 +364,11 @@ static void savic_setup(void)
>  	 * VMRUN, the hypervisor makes use of this information to make sure
>  	 * the APIC backing page is mapped in NPT.
>  	 */
> -	res = savic_register_gpa(gpa);
> +	if (hv_isolation_type_snp())
> +		res = hv_set_savic_backing_page(gfn);
> +	else
> +		res = savic_register_gpa(gpa);
> +

This is ugly and doesn't belong here.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette