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    Subject[PATCH 09/24] x86/mm/kaiser: Map the espfix structures
    Date
    From: Dave Hansen <dave.hansen@linux.intel.com>

    There is some rather arcane code to help when an IRET returns
    to 16-bit segments. It is referred to as the "espfix" code.
    This consists of a few per-CPU variables:

    espfix_stack: tells us where the stack is allocated (the bottom)

    espfix_waddr: tells us to where %rsp may be pointed (the top)

    These are in addition to the stack itself. All three things must
    be mapped for the espfix code to function.

    Note: the espfix code runs with a kernel GSBASE, but user
    (shadow) page tables. A switch to the kernel page tables could
    be performed instead of mapping these structures, but mapping
    them is simpler and less likely to break the assembly. To switch
    over to the kernel copy, additional temporary storage would be
    required which is in short supply in this context.

    The original KAISER patch missed this case.

    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: daniel.gruss@iaik.tugraz.at
    Cc: hughd@google.com
    Cc: keescook@google.com
    Cc: linux-mm@kvack.org
    Cc: michael.schwarz@iaik.tugraz.at
    Cc: moritz.lipp@iaik.tugraz.at
    Cc: richard.fellner@student.tugraz.at
    Link: https://lkml.kernel.org/r/20171123003457.EB854D0D@viggo.jf.intel.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/kernel/espfix_64.c | 12 +++++++++---
    1 file changed, 9 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
    index 7b95cb47a3cf..319033f5bbd9 100644
    --- a/arch/x86/kernel/espfix_64.c
    +++ b/arch/x86/kernel/espfix_64.c
    @@ -33,6 +33,7 @@

    #include <linux/init.h>
    #include <linux/init_task.h>
    +#include <linux/kaiser.h>
    #include <linux/kernel.h>
    #include <linux/percpu.h>
    #include <linux/gfp.h>
    @@ -41,7 +42,6 @@
    #include <asm/pgalloc.h>
    #include <asm/setup.h>
    #include <asm/espfix.h>
    -#include <asm/kaiser.h>

    /*
    * Note: we only need 6*8 = 48 bytes for the espfix stack, but round
    @@ -61,8 +61,8 @@
    #define PGALLOC_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO)

    /* This contains the *bottom* address of the espfix stack */
    -DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
    -DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);
    +DEFINE_PER_CPU_USER_MAPPED(unsigned long, espfix_stack);
    +DEFINE_PER_CPU_USER_MAPPED(unsigned long, espfix_waddr);

    /* Initialization mutex - should this be a spinlock? */
    static DEFINE_MUTEX(espfix_init_mutex);
    @@ -226,4 +226,10 @@ void init_espfix_ap(int cpu)
    per_cpu(espfix_stack, cpu) = addr;
    per_cpu(espfix_waddr, cpu) = (unsigned long)stack_page
    + (addr & ~PAGE_MASK);
    + /*
    + * _PAGE_GLOBAL is not really required. This is not a hot
    + * path, but we do it here for consistency.
    + */
    + kaiser_add_mapping((unsigned long)stack_page, PAGE_SIZE,
    + __PAGE_KERNEL | _PAGE_GLOBAL);
    }
    --
    2.14.1
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