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In the LBR call stack mode, LBR information is used to reconstruct a call stack. To get the complete call stack, perf has to save/restore all LBR registers during a context switch. Due to a large number of the LBR registers, this process causes a high CPU overhead. To reduce the CPU overhead during a context switch, use the XSAVES/XRSTORS instructions. Every XSAVE area must follow a canonical format: the legacy region, an XSAVE header and the extended region. Although the LBR information is only kept in the extended region, a space for the legacy region and XSAVE header is still required. Add a new dedicated structure for LBR XSAVES support. Before enabling XSAVES support, the size of the LBR state has to be sanity checked, because: - the size of the software structure is calculated from the max number of the LBR depth, which is enumerated by the CPUID leaf for Arch LBR. The size of the LBR state is enumerated by the CPUID leaf for XSAVE support of Arch LBR. If the values from the two CPUID leaves are not consistent, it may trigger a buffer overflow. For example, a hypervisor may unconsciously set inconsistent values for the two emulated CPUID. - unlike other state components, the size of an LBR state depends on the max number of LBRs, which may vary from generation to generation. Expose the function xfeature_size() for the sanity check. The LBR XSAVES support will be disabled if the size of the LBR state enumerated by CPUID doesn't match with the size of the software structure. The XSAVE instruction requires 64-byte alignment for state buffers. A new macro is added to reflect the alignment requirement. A 64-byte aligned kmem_cache is created for architecture LBR. Currently, the structure for each state component is maintained in fpu/types.h. The structure for the new LBR state component should be maintained in the same place. Move structure lbr_entry to fpu/types.h as well for broader sharing. Add dedicated lbr_save/lbr_restore functions for LBR XSAVES support, which invokes the corresponding xstate helpers to XSAVES/XRSTORS LBR information at the context switch when the call stack mode is enabled. Since the XSAVES/XRSTORS instructions will be eventually invoked, the dedicated functions is named with '_xsaves'/'_xrstors' postfix. Signed-off-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dave Hansen <dave.hansen@intel.com> Link: https://lkml.kernel.org/r/1593780569-62993-23-git-send-email-kan.liang@linux.intel.com |
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| bugs.c | ||
| core.c | ||
| init.c | ||
| Makefile | ||
| regset.c | ||
| signal.c | ||
| xstate.c | ||