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From:   Yazen Ghannam <yazen.ghannam@amd.com>
To:     <linux-edac@vger.kernel.org>
CC:     <linux-kernel@vger.kernel.org>, <tony.luck@intel.com>,
        <x86@kernel.org>, Yazen Ghannam <yazen.ghannam@amd.com>
Subject: [PATCH 1/2] x86/mce: Disable preemption for CPER decoding
Date:   Thu, 22 Jun 2023 08:18:40 -0500
Message-ID: <20230622131841.3153672-2-yazen.ghannam@amd.com>
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Scalable MCA systems may report errors found during boot-time polling
through the ACPI Boot Error Record Table (BERT). The errors are logged
in an "x86 Processor" Common Platform Error Record (CPER). The format of
the x86 CPER does not include a logical CPU number, but it does provide
the logical APIC ID for the logical CPU. Also, it does not explicitly
provide MCA error information, but it can share this information using
an "MSR Context" defined in the CPER format.

The MCA error information is parsed by
1) Checking that the context matches the Scalable MCA register space.
2) Finding the logical CPU that matches the logical APIC ID from the
   CPER.
3) Filling in struct mce with the relevant data and logging it.

All the above is done when the BERT is processed during late init. This
can be scheduled on any CPU, and it may be preemptible.

This results in two issues.
1) mce_setup() includes a call to smp_processor_id(). This will throw a
   warning if preemption is enabled.
2) mce_setup() will pull info from the executing CPU, so some info in
   struct mce may be incorrect for the CPU with the error. For example,
   in a dual-socket system, an error logged in socket 1 CPU but
   processed by a socket 0 CPU will save the PPIN of the socket 0 CPU.

Fix the first issue by locally disabling preemption before calling
mce_setup().

Fixes: 4a24d80b8c3e ("x86/mce, cper: Pass x86 CPER through the MCA handling chain")
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Cc: stable@vger.kernel.org
---
 arch/x86/kernel/cpu/mce/apei.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kernel/cpu/mce/apei.c b/arch/x86/kernel/cpu/mce/apei.c
index 8ed341714686..2a7a51ca2995 100644
--- a/arch/x86/kernel/cpu/mce/apei.c
+++ b/arch/x86/kernel/cpu/mce/apei.c
@@ -97,7 +97,9 @@ int apei_smca_report_x86_error(struct cper_ia_proc_ctx *ctx_info, u64 lapic_id)
 	if (ctx_info->reg_arr_size < 48)
 		return -EINVAL;
 
+	get_cpu();
 	mce_setup(&m);
+	put_cpu();
 
 	m.extcpu = -1;
 	m.socketid = -1;
-- 
2.34.1