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    SubjectRe: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)
    On Fri, Jan 5, 2018 at 1:14 PM, Jiri Kosina <jikos@kernel.org> wrote:
    > On Fri, 5 Jan 2018, Dave Hansen wrote:
    >
    >> >>> --- a/arch/x86/platform/efi/efi_64.c
    >> >>> +++ b/arch/x86/platform/efi/efi_64.c
    >> >>> @@ -95,6 +95,12 @@ pgd_t * __init efi_call_phys_prolog(void
    >> >>> save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE);
    >> >>> vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
    >> >>> set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
    >> >>> + /*
    >> >>> + * pgprot API doesn't clear it for PGD
    >> >>> + *
    >> >>> + * Will be brought back automatically in _epilog()
    >> >>> + */
    >> >>> + pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX;
    >> >>> }
    >> >>> __flush_tlb_all();
    >> >>
    >> >> Wait a sec... Where does the _PAGE_USER come from? Shouldn't we see
    >> >> the &init_mm in there and *not* set _PAGE_USER?
    >> >
    >> > That's because pgd_populate() uses _PAGE_TABLE and not _KERNPG_TABLE for
    >> > reasons that are behind me.

    Oh, I completely missed that; and then the issue would have got hidden
    by one of my later per-process-kaiser patches.

    >> >
    >> > I did put this on my TODO list, but for later.
    >> >
    >> > (and yes, I tried clearing _PAGE_USER from init_mm's PGD, and no obvious
    >> > breakages appeared, but I wanted to give it more thought later).
    >>
    >> Feel free to add my Ack on this.

    And mine - thanks a lot for dealing with this Jiri.

    >
    > Thanks. I'll extract the patch out of this thread and submit it
    > separately, so that it doesn't get lost buried here.
    >
    >> I'd personally much rather muck with random relatively unused bits of
    >> the efi code than touch the core PGD code.
    >
    > Exactly. Especially at this point.

    Indeed.

    >
    >> We need to go look at it again in the 4.16 timeframe, probably.
    >
    > Agreed. On my TODO list already.
    >
    > Thanks,
    >
    > --
    > Jiri Kosina
    > SUSE Labs
    >

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