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Wed, 12 Aug 2026 08:18:09 -0700 (PDT) From: Shaikh Kamaluddin To: Davidlohr Bueso , Jonathan Cameron , Dave Jiang , Alison Schofield , Vishal Verma , Dan Williams , Ira Weiny , Li Ming , Ben Cheatham , tony.luck@intel.com, bp@alien8.de Cc: linux-cxl@vger.kernel.org, linux-edac@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, x86@kernel.org Subject: [PATCH v2] cxl/mce: Avoid alias page retirement for corrected errors Date: Wed, 12 Aug 2026 20:47:59 +0530 Message-ID: <20260812151759.14390-1-shaikhkamal2012@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit cxl_handle_mce() offlines the aliased page of an Extended Linear Cache (ELC) region for any MCE with a usable address in the region. This includes corrected errors and non-memory errors, needlessly reducing usable memory. Restrict ELC MCE handling to uncorrected memory errors. Use mce_is_correctable() so that MCE_AR_SEVERITY errors continue to retire the alias when the reported page is handled elsewhere. Fixes: 516e5bd0b6bf ("cxl: Add mce notifier to emit aliased address for extended linear cache") Signed-off-by: Shaikh Kamaluddin --- Changelog: v1 -> v2: - Reworked commit message per review feedback - Dropped redundant comment from the code Reproduced under QEMU/vng. QEMU's cxl-type3 does not emulate the HMAT extended-linear address_mode bit, so ELC was forced locally for testing via a one-line debug hack in cxl_region_probe() (not part of this patch): if (!p->cache_size && p->res) p->cache_size = resource_size(p->res) / 2; Steps: 1. Boot with an Intel CPU model under TCG (KVM host-passthrough will otherwise leak the host's real vendor ID, and AMD/SMCA takes a different mce_usable_address() path than the one under test): vng -v -r ./arch/x86/boot/bzImage --disable-kvm --qemu-opts='-cpu Skylake-Server-v4,+mce,+mca -m 4G -machine q35,cxl=on -object memory-backend-ram,id=cxl-mem0,size=512M -device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.0 -device cxl-rp,port=0,bus=cxl.0,id=root_port0,chassis=0,slot=0 -device cxl-type3,bus=root_port0,volatile-memdev=cxl-mem0,id=cxl-mem-device0 -M cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.size=512M' 2. modprobe mce-inject $cxl list -M $cxl list -D $cxl create-region -m mem0 -d decoder0.0 -w 1 -g 256 -t ram $dmesg | grep "DEBUG: forced cache_size" $modprobe device_dax $modprobe kmem $ls /sys/bus/dax/devices/ $daxctl reconfigure-device dax0.0 --mode=system-ram $lsmem it will show as below: dax0.0 [ 42.857642] Fallback order for Node 0: 0 [ 42.857828] Built 1 zonelists, mobility grouping on. Total pages: 1010805 [ 42.858446] Policy zone: Normal [ { "chardev":"dax0.0", "size":536870912, "target_node":0, "align":2097152, "mode":"system-ram", "online_memblocks":4, "total_memblocks":4, "movable":true } ] reconfigured 1 device RANGE SIZE STATE REMOVABLE BLOCK 0x0000000000000000-0x000000007fffffff 2G online yes 0-15 0x0000000100000000-0x000000017fffffff 2G online yes 32-47 0x0000000190000000-0x00000001afffffff 512M online yes 50-53 Memory block size: 128M Total online memory: 4.5G Total offline memory: 0B 3. Load the injector if not loaded earlier and derive the two MCi_STATUS values. modprobe mce-inject MCi_STATUS bit layout used here (arch/x86/include/asm/mce.h): bit 63 VAL - record valid bit 61 UC - uncorrected (0 = corrected error under test) bit 60 EN - error reporting enabled bit 59 MISCV - MCi_MISC valid bit 58 ADDRV - MCi_ADDR valid bits[15:0] MCACOD - bit 7 set = memory-error signature, per mce_is_memory_error()'s Intel branch python3 -c " VAL, UC, EN, MISCV, ADDRV = 1<<63, 1<<61, 1<<60, 1<<59, 1<<58 MCACOD_MEM = 1<<7 # memory error signature ce = VAL | EN | MISCV | ADDRV | MCACOD_MEM uc = ce | UC print(f'CE status = {hex(ce)}') print(f'UC status = {hex(uc)}')" # CE status = 0x9c00000000000080 # UC status = 0xbc00000000000080 MCi_MISC: address-mode field, bits[8:6], must be 2 (physical): python3 -c "print(hex(2 << 6))" # misc = 0x80 4. $ cd /sys/kernel/debug/mce-inject $echo sw > flags $echo 0x9C00000000000080 > status $echo 0x80 > misc $echo 0x190010000 > addr $echo 9 > bank [ 221.813395] mce: [Hardware Error]: Machine check events logged [ 221.814716] cxl_mce_debug: entered status=0x9c00000000000080 addr=0x190010000 cache_size=0x10000000 res=[mem 0x190000000-0x1afffffff flags 0x200] usable=1 [ 221.816200] cxl_mce_debug: spa=0x190010000 contains=1 [ 221.817089] cxl_mce_debug: spa_alias=0x1a0010000 pfn=0x1a0010 pfn_valid=1 [ 221.817655] cxl_region region0: Offlining aliased SPA address0: 0x1a0010000 [ 221.821504] Memory failure: 0x1a0010: recovery action for free buddy page: Recovered [ 221.823903] mce: [Hardware Error]: CPU 0: Machine Check: 0 Bank 9: 9c00000000000080 [ 221.824617] mce: [Hardware Error]: TSC a605ccda40 ADDR 190010000 MISC 80 [ 221.824997] mce: [Hardware Error]: PROCESSOR 0:50654 TIME 1786375908 SOCKET 0 APIC 0 microcode 1 root@virtme-ng:/sys/kernel/debug/mce-inject# root@virtme-ng:/sys/kernel/debug/mce-inject# grep HardwareCorrupted /proc/meminfo HardwareCorrupted: 4 kB CE without this patch: cxl_region region0: Offlining aliased SPA address0: 0x1a0010000 Memory failure: 0x1a0010: recovery action for free buddy page: Recovered HardwareCorrupted: 4 kB ------------------------------------- CE with this patch: (no "Offlining aliased SPA" message logged) HardwareCorrupted: 0 kB $cd /sys/kernel/debug/mce-inject $echo sw > flags $echo 0x9C00000000000080 > status $echo 0x80 > misc $echo 0x190010000 > addr $echo 9 > bank addr bank cpu flags ipid misc README status synd [ 61.681659] mce: [Hardware Error]: Machine check events logged [ 61.683442] cxl_mce_debug: entered status=0x9c00000000000080 addr=0x190010000 cache_size=0x10000000 res=[mem 0x190000000-0x1afffffff flags 0x200] usable=1 [ 61.684528] mce: [Hardware Error]: CPU 0: Machine Check: 0 Bank 9: 9c00000000000080 [ 61.684974] mce: [Hardware Error]: TSC 2eeae32fe0 ADDR 190010000 MISC 80 [ 61.688880] mce: [Hardware Error]: PROCESSOR 0:50654 TIME 1786377156 SOCKET 0 APIC 0 microcode 1 [ 86.504456] clocksource: Watchdog remote CPU 11 read timed out $grep HardwareCorrupted /proc/meminfo HardwareCorrupted: 0 kB ------------------------- For UC, same steps only status bit information will change : $cd /sys/kernel/debug/mce-inject $echo sw > flags $echo 0xbc00000000000080 > status $echo 0x80 > misc $echo 0x190010000 > addr $echo 9 > bank $dmesg | grep cxl_mce_debug $grep HardwareCorrupted /proc/meminfo [ 313.398747] mce: [Hardware Error]: Machine check events logged [ 313.400518] cxl_mce_debug: entered status=0xbc00000000000080 addr=0x190010000 cache_size=0x10000000 res=[mem 0x190000000-0x1afffffff flags 0x200] usable=1 [ 313.401727] cxl_mce_debug: spa=0x190010000 contains=1 [ 313.402157] cxl_mce_debug: spa_alias=0x1a0010000 pfn=0x1a0010 pfn_valid=1 [ 313.402663] cxl_region region0: Offlining aliased SPA address0: 0x1a0010000 [ 313.405999] Memory failure: 0x1a0010: recovery action for free buddy page: Recovered [ 313.408375] mce: [Hardware Error]: CPU 0: Machine Check: 0 Bank 9: bc00000000000080 [ 313.408999] mce: [Hardware Error]: TSC e9dd2869e0 ADDR 190010000 MISC 80 [ 313.409367] mce: [Hardware Error]: PROCESSOR 0:50654 TIME 1786377750 SOCKET 0 APIC 0 microcode 1 Patched, UC: alias still offlined, confirming uncorrected handling is unchanged by this patch. cxl_region region0: Offlining aliased SPA address0: 0x1a0010000 Memory failure: 0x1a0010: recovery action for free buddy page: Recovered HardwareCorrupted: 4 kB drivers/cxl/core/mce.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/cxl/core/mce.c b/drivers/cxl/core/mce.c index 65fed913b221..e3c561489a00 100644 --- a/drivers/cxl/core/mce.c +++ b/drivers/cxl/core/mce.c @@ -18,7 +18,13 @@ static int cxl_handle_mce(struct notifier_block *nb, unsigned long val, u64 spa, spa_alias; unsigned long pfn; - if (!mce || !mce_usable_address(mce)) + if (!mce) + return NOTIFY_DONE; + + if (!mce_is_memory_error(mce) || mce_is_correctable(mce)) + return NOTIFY_DONE; + + if (!mce_usable_address(mce)) return NOTIFY_DONE; spa = mce->addr & MCI_ADDR_PHYSADDR; base-commit: 7098e9cd98a05c0c5de2fae0c2465f9d966fdd07 -- 2.43.0