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    selftests/vm/pkeys: exercise x86 XSAVE init state · d892454b
    Dave Hansen 提交于
    On x86, there is a set of instructions used to save and restore register
    state collectively known as the XSAVE architecture.  There are about a
    dozen different features managed with XSAVE.  The protection keys
    register, PKRU, is one of those features.
    
    The hardware optimizes XSAVE by tracking when the state has not changed
    from its initial (init) state.  In this case, it can avoid the cost of
    writing state to memory (it would usually just be a bunch of 0's).
    
    When the pkey register is 0x0 the hardware optionally choose to track the
    register as being in the init state (optimize away the writes).  AMD CPUs
    do this more aggressively compared to Intel.
    
    On x86, PKRU is rarely in its (very permissive) init state.  Instead, the
    value defaults to something very restrictive.  It is not surprising that
    bugs have popped up in the rare cases when PKRU reaches its init state.
    
    Add a protection key selftest which gets the protection keys register into
    its init state in a way that should work on Intel and AMD.  Then, do a
    bunch of pkey register reads to watch for inadvertent changes.
    
    This adds "-mxsave" to CFLAGS for all the x86 vm selftests in order to
    allow use of the XSAVE instruction __builtin functions.  This will make
    the builtins available on all of the vm selftests, but is expected to be
    harmless.
    
    Link: https://lkml.kernel.org/r/20210611164202.1849B712@viggo.jf.intel.comSigned-off-by: NDave Hansen <dave.hansen@linux.intel.com>
    Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
    Tested-by: NAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Cc: Ram Pai <linuxram@us.ibm.com>
    Cc: Sandipan Das <sandipan@linux.ibm.com>
    Cc: Florian Weimer <fweimer@redhat.com>
    Cc: "Desnes A. Nunes do Rosario" <desnesn@linux.vnet.ibm.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: Michal Hocko <mhocko@kernel.org>
    Cc: Michal Suchanek <msuchanek@suse.de>
    Cc: Shuah Khan <shuah@kernel.org>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    d892454b
pkey-x86.h 3.5 KB