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81e3cbdef2
When decoding an instruction or handling a perf event that references an LDT segment, if we don't have a valid user context, trying to access the LDT by any means other than SLDT is racy. Certainly, using current->active_mm is wrong, as active_mm can point to a real user mm when CR3 and LDTR no longer reference that mm. Clean up the code. If nmi_uaccess_okay() says we don't have a valid context, just fail. Otherwise use current->mm. Signed-off-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Rik van Riel <riel@surriel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: https://lore.kernel.org/r/20250402094540.3586683-3-mingo@kernel.org