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

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Message-ID: <20250116061224.1701-1-namjain@linux.microsoft.com>
Date: Thu, 16 Jan 2025 06:12:24 +0000
From: Naman Jain <namjain@...ux.microsoft.com>
To: "K . Y . Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org
Cc: linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Saurabh Sengar <ssengar@...ux.microsoft.com>
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