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    SubjectRe: [PATCH] x86_64: disable identity mappings statically
    On Fri, Feb 11, 2011 at 08:46:41AM -0800, Eric W. Biederman wrote:
    > Jiri Olsa <jolsa@redhat.com> writes:
    >
    > > hi,
    > >
    > > while browsing the page table setup code, I noticed the x86_64 head
    > > code might not need the identity mappings at all.
    > > It seems it's ok to switch it off completely from the begining,
    > > unless I'm missing something.
    >
    > Have you tested it?

    yes, I booted it with no problem

    >
    > I expect you will find that we need the identity mapping because
    > before we load this page table we are running with virt==phys
    > and we need the identity mapping retained in the new page table
    > so we can get to the instruction after movq %rax, %cr0.

    well, right after the page table setup, there's following code
    switching to the kernel map adresses 0xffffffff80000000+

    movq %rax, %cr3

    /* Ensure I am executing from virtual addresses */
    movq $1f, %rax
    jmp *%rax
    1:


    and I found no other identity mapping usage after this point

    jirka


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