linux-kernel - [PATCH] x86/hyperv/vtl: Stop kernel from probing VTL0 low memory

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Message-Id: <20250117170141.1351283-1-romank@linux.microsoft.com>
Date: Fri, 17 Jan 2025 09:01:41 -0800
From: Roman Kisel <romank@...ux.microsoft.com>
To: namjain@...ux.microsoft.com
Cc: bp@...en8.de,
	dave.hansen@...ux.intel.com,
	decui@...rosoft.com,
	haiyangz@...rosoft.com,
	kys@...rosoft.com,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	mingo@...hat.com,
	ssengar@...ux.microsoft.com,
	tglx@...utronix.de,
	wei.liu@...nel.org,
	x86@...nel.org
Subject: [PATCH] x86/hyperv/vtl: Stop kernel from probing VTL0 low memory

> For Linux, running in Hyper-V VTL (Virtual Trust Level), kernel in VTL2
> tries to access VTL0 low memory in probe_roms. This memory is not
> described in the e820 map. Initialize probe_roms call to no-ops
> during boot for VTL2 kernel to avoid this. The issue got identified
> in OpenVMM which detects invalid accesses initiated from kernel running
> in VTL2.
> 
> Co-developed-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_vtl.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 4e1b1e3b5658..3f4e20d7b724 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -30,6 +30,7 @@ void __init hv_vtl_init_platform(void)
>	x86_platform.realmode_init = x86_init_noop;
>	x86_init.irqs.pre_vector_init = x86_init_noop;
>	x86_init.timers.timer_init = x86_init_noop;
> +	x86_init.resources.probe_roms = x86_init_noop;
>  
>	/* Avoid searching for BIOS MP tables */
>	x86_init.mpparse.find_mptable = x86_init_noop;
> 
> base-commit: 37136bf5c3a6f6b686d74f41837a6406bec6b7bc
> -- 
> 2.43.0

Thanks, Naman!

Tested-by: Roman Kisel <romank@...ux.microsoft.com>
Reviewed-by: Roman Kisel <romank@...ux.microsoft.com>