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perf/x86/intel/lbr: Zero the xstate buffer on allocation

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[ Upstream commit 7f049fbdd5 ]

XRSTORS requires a valid xstate buffer to work correctly. XSAVES does not
guarantee to write a fully valid buffer according to the SDM:

  "XSAVES does not write to any parts of the XSAVE header other than the
   XSTATE_BV and XCOMP_BV fields."

XRSTORS triggers a #GP:

  "If bytes 63:16 of the XSAVE header are not all zero."

It's dubious at best how this can work at all when the buffer is not zeroed
before use.

Allocate the buffers with __GFP_ZERO to prevent XRSTORS failure.

Fixes: ce711ea3ca ("perf/x86/intel/lbr: Support XSAVES/XRSTORS for LBR context switch")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/87wnr0wo2z.ffs@nanos.tec.linutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Thomas Gleixner 2021-06-11 15:03:16 +02:00 • committed by Sasha Levin
commit 4df9ed0edb
1 changed files with 2 additions and 1 deletions
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3
arch/x86/events/intel/lbr.c
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@ -730,7 +730,8 @@ void reserve_lbr_buffers(void)
if (!kmem_cache || cpuc->lbr_xsave)
continue;
cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache, GFP_KERNEL,
cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache,
GFP_KERNEL | __GFP_ZERO,
cpu_to_node(cpu));
}
}