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Subject[tip:x86/urgent] x86/boot: Fix boot failure when SMP MP-table is based at 0
Commit-ID:  ac5292e9a294618cecb31109d1ba265e3d027ba2
Gitweb: https://git.kernel.org/tip/ac5292e9a294618cecb31109d1ba265e3d027ba2
Author: Tom Lendacky <thomas.lendacky@amd.com>
AuthorDate: Mon, 6 Nov 2017 14:17:53 -0600
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 17 Nov 2017 15:30:33 +0100

x86/boot: Fix boot failure when SMP MP-table is based at 0

When crosvm is used to boot a kernel as a VM, the SMP MP-table is found
at physical address 0x0. This causes mpf_base to be set to 0 and a
subsequent "if (!mpf_base)" check in default_get_smp_config() results in
the MP-table not being parsed. Further into the boot this results in an
oops when attempting a read_apic_id().

Add a boolean variable that is set to true when the MP-table is found.
Use this variable for testing if the MP-table was found so that even a
value of 0 for mpf_base will result in continued parsing of the MP-table.

Fixes: 5997efb96756 ("x86/boot: Use memremap() to map the MPF and MPC data")
Reported-by: Tomeu Vizoso <tomeu@tomeuvizoso.net>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: regression@leemhuis.info
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20171106201753.23059.86674.stgit@tlendack-t1.amdoffice.net

---
arch/x86/kernel/mpparse.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/mpparse.c b/arch/x86/kernel/mpparse.c
index 410c5da..3a4b128 100644
--- a/arch/x86/kernel/mpparse.c
+++ b/arch/x86/kernel/mpparse.c
@@ -431,6 +431,7 @@ static inline void __init construct_default_ISA_mptable(int mpc_default_type)
}

static unsigned long mpf_base;
+static bool mpf_found;

static unsigned long __init get_mpc_size(unsigned long physptr)
{
@@ -504,7 +505,7 @@ void __init default_get_smp_config(unsigned int early)
if (!smp_found_config)
return;

- if (!mpf_base)
+ if (!mpf_found)
return;

if (acpi_lapic && early)
@@ -593,6 +594,7 @@ static int __init smp_scan_config(unsigned long base, unsigned long length)
smp_found_config = 1;
#endif
mpf_base = base;
+ mpf_found = true;

pr_info("found SMP MP-table at [mem %#010lx-%#010lx] mapped at [%p]\n",
base, base + sizeof(*mpf) - 1, mpf);
@@ -858,7 +860,7 @@ static int __init update_mp_table(void)
if (!enable_update_mptable)
return 0;

- if (!mpf_base)
+ if (!mpf_found)
return 0;

mpf = early_memremap(mpf_base, sizeof(*mpf));
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