Re: [PATCH] cxl: Fix CXL_HEADERLOG_SIZE to match RAS Capability size

[Alison Schofield]

On Fri, Jun 05, 2026 at 01:06:10PM -0500, Terry Bowman wrote:
> The CXL r4.0 8.2.4.17.7 RAS Capability Structure has total length 0x58
> bytes (CXL_RAS_CAPABILITY_LENGTH); the Header Log occupies the trailing
> 64 bytes at offset 0x18.  CXL_HEADERLOG_SIZE was defined as SZ_512,
> eight times the actual on-device size.
> 
> header_log_copy() reads CXL_HEADERLOG_SIZE_U32 (128) dwords from the
> RAS capability iomap, overrunning the 88-byte mapping by 448 bytes.
> The cxl_aer_uncorrectable_error trace event memcpy()s CXL_HEADERLOG_SIZE
> (512) bytes from its source.  For the CPER caller the source is
> struct cxl_ras_capability_regs::header_log[16] (64 bytes) embedded in a
> stack-local cxl_cper_prot_err_work_data, so the memcpy reads 448 bytes
> of kernel stack into the trace event ring buffer where userspace can
> read it via tracefs.
> 
> Set CXL_HEADERLOG_SIZE to 64 and derive CXL_HEADERLOG_SIZE_U32 from it,
> bringing all iomap readers into agreement on 16 dwords.  Userspace tools
> such as rasdaemon have grown a dependency on the buggy 512-byte (128 u32)
> header_log layout in the cxl_aer_uncorrectable_error trace event.  Add
> CXL_HEADERLOG_TRACE_SIZE_U32 = 128 and use it for the trace event
> __array and its memcpy to preserve that ABI.  Both callers now pass a
> zero-filled u32[CXL_HEADERLOG_TRACE_SIZE_U32] staging buffer with only
> the first CXL_HEADERLOG_SIZE_U32 (16) entries populated from hardware;
> the remaining 112 u32s are zero-padded, keeping the 512-byte trace ring
> buffer layout intact.


Reviewed-by: Alison Schofield <alison.schofield@xxxxxxxxx>