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    x86/pti: Fix !PCID and sanitize defines · f10ee3dc
    Thomas Gleixner 提交于
    The switch to the user space page tables in the low level ASM code sets
    unconditionally bit 12 and bit 11 of CR3. Bit 12 is switching the base
    address of the page directory to the user part, bit 11 is switching the
    PCID to the PCID associated with the user page tables.
    
    This fails on a machine which lacks PCID support because bit 11 is set in
    CR3. Bit 11 is reserved when PCID is inactive.
    
    While the Intel SDM claims that the reserved bits are ignored when PCID is
    disabled, the AMD APM states that they should be cleared.
    
    This went unnoticed as the AMD APM was not checked when the code was
    developed and reviewed and test systems with Intel CPUs never failed to
    boot. The report is against a Centos 6 host where the guest fails to boot,
    so it's not yet clear whether this is a virt issue or can happen on real
    hardware too, but thats irrelevant as the AMD APM clearly ask for clearing
    the reserved bits.
    
    Make sure that on non PCID machines bit 11 is not set by the page table
    switching code.
    
    Andy suggested to rename the related bits and masks so they are clearly
    describing what they should be used for, which is done as well for clarity.
    
    That split could have been done with alternatives but the macro hell is
    horrible and ugly. This can be done on top if someone cares to remove the
    extra orq. For now it's a straight forward fix.
    
    Fixes: 6fd166aa ("x86/mm: Use/Fix PCID to optimize user/kernel switches")
    Reported-by: NLaura Abbott <labbott@redhat.com>
    Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: stable <stable@vger.kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Willy Tarreau <w@1wt.eu>
    Cc: David Woodhouse <dwmw@amazon.co.uk>
    Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801140009150.2371@nanos
    f10ee3dc
calling.h 9.4 KB