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Re: [PATCH] x86/mcheck: allow varying bank counts per CPU
- To: Soham Dandapat <Soham.Dandapat@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Fri, 5 Sep 2025 13:02:13 -0400
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Fri, 05 Sep 2025 17:02:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-09-05 12:52, Soham Dandapat wrote:
In mca_cap_init function,the mcabanks_alloc allocates and
initializes an mca_banks structure for managing MCA banks,
setting up a bank map and storing the specified or default number
of banks.
After this we will call mcabanks_set(i, mca_allbanks);
The mcabanks_set function sets a specific bit in the bank_map of
an mca_banks structure, provided the structure, its bank_map, and
the bit index are valid.
At the end, we will call
mcabanks_free(xchg(&mca_allbanks, all));
This function is thread safe and does below:
1. Atomically exchanges the value of "mca_allbanks" with "all"
2. Returns the old value that was previously in "mca_allbanks"
So, when we will call mcabanks_free , that will free the memory.
The problem is that mcabanks_set(i, mca_allbanks) function is updating
mca_allbanks which will be freed via mcabanks_free later. This means
new mca_allbanks instance("all") will never get chance to update
it's bank_map.
Due to this when we will collect log from mcheck_mca_logout function ,
the condition "if ( !mcabanks_test(i, bankmask) )" will always fails
and MCA logs will not be collected for any bank.
The fix is to solve this problem.
Fixes: 560cf418c845 ("x86/mcheck: allow varying bank counts per CPU")
Signed-off-by: Soham Dandapat <soham.dandapat@xxxxxxx>
Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
Maybe the patch subject should be "x86/mcheck: Fix mca bank
initialization" to differentiate from the Fixes commit?
Thanks,
Jason
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