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

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Date:   Fri,  2 Jun 2023 05:41:52 -0700
From:   Saurabh Sengar <ssengar@...ux.microsoft.com>
To:     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: [PATCH] x86/hyperv: add noop functions to x86_init mpparse functions

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;
+
 	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