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ricardonbp3tk0v
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cacheinfo: Allocate memory during CPU hotplug if not done from the primary CPU
Commit 5944ce0 ("arch_topology: Build cacheinfo from primary CPU") adds functionality that architectures can use to optionally allocate and build cacheinfo early during boot. Commit 6539cff ("cacheinfo: Add arch specific early level initializer") lets secondary CPUs correct (and reallocate memory) cacheinfo data if needed. If the early build functionality is not used and cacheinfo does not need correction, memory for cacheinfo is never allocated. x86 does not use the early build functionality. Consequently, during the cacheinfo CPU hotplug callback, last_level_cache_is_valid() attempts to dereference a NULL pointer: BUG: kernel NULL pointer dereference, address: 0000000000000100 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not present page PGD 0 P4D 0 Oops: 0000 [#1] PREEPMT SMP NOPTI CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1 RIP: 0010: last_level_cache_is_valid+0x95/0xe0a Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if not done earlier. Moreover, before determining the validity of the last-level cache info, ensure that it has been allocated. Simply checking for non-zero cache_leaves() is not sufficient, as some architectures (e.g., Intel processors) have non-zero cache_leaves() before allocation. Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size(). This function iterates over all online CPUs. However, a CPU may have come online recently, but its cacheinfo may not have been allocated yet. While here, remove an unnecessary indentation in allocate_cache_info(). [ bp: Massage. ] Fixes: 6539cff ("cacheinfo: Add arch specific early level initializer") Signed-off-by: Ricardo Neri <[email protected]> Signed-off-by: Borislav Petkov (AMD) <[email protected]> Reviewed-by: Radu Rendec <[email protected]> Reviewed-by: Nikolay Borisov <[email protected]> Reviewed-by: Andreas Herrmann <[email protected]> Reviewed-by: Sudeep Holla <[email protected]> Cc: [email protected] # 6.3+ Link: https://lore.kernel.org/r/[email protected]
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drivers/base/cacheinfo.c

Lines changed: 8 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -58,7 +58,7 @@ bool last_level_cache_is_valid(unsigned int cpu)
5858
{
5959
struct cacheinfo *llc;
6060

61-
if (!cache_leaves(cpu))
61+
if (!cache_leaves(cpu) || !per_cpu_cacheinfo(cpu))
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return false;
6363

6464
llc = per_cpu_cacheinfo_idx(cpu, cache_leaves(cpu) - 1);
@@ -458,11 +458,9 @@ int __weak populate_cache_leaves(unsigned int cpu)
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return -ENOENT;
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}
460460

461-
static inline
462-
int allocate_cache_info(int cpu)
461+
static inline int allocate_cache_info(int cpu)
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{
464-
per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu),
465-
sizeof(struct cacheinfo), GFP_ATOMIC);
463+
per_cpu_cacheinfo(cpu) = kcalloc(cache_leaves(cpu), sizeof(struct cacheinfo), GFP_ATOMIC);
466464
if (!per_cpu_cacheinfo(cpu)) {
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cache_leaves(cpu) = 0;
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return -ENOMEM;
@@ -534,7 +532,11 @@ static inline int init_level_allocate_ci(unsigned int cpu)
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*/
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ci_cacheinfo(cpu)->early_ci_levels = false;
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537-
if (cache_leaves(cpu) <= early_leaves)
535+
/*
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* Some architectures (e.g., x86) do not use early initialization.
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* Allocate memory now in such case.
538+
*/
539+
if (cache_leaves(cpu) <= early_leaves && per_cpu_cacheinfo(cpu))
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return 0;
539541

540542
kfree(per_cpu_cacheinfo(cpu));

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