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    SubjectRe: [PATCH] arm64: fixmap: fix missing sub-page offset for earlyprintk
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    On Mon, Apr 28, 2014 at 1:50 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:
    > Commit d57c33c5daa4 (add generic fixmap.h) added (among other
    > similar things) set_fixmap_io to deal with early ioremap of devices.
    >
    > More recently, commit bf4b558eba92 (arm64: add early_ioremap support)
    > converted the arm64 earlyprintk to use set_fixmap_io. A side effect of
    > this conversion is that my virtual machines have stopped booting when
    > I pass "earlyprintk=uart8250-8bit,0x3f8" to the guest kernel.
    >
    > Turns out that the new earlyprintk code doesn't care at all about
    > sub-page offsets, and just assumes that the earlyprintk device will
    > be page-aligned. Obviously, that doesn't play well with the above example.
    >
    > Further investigation shows that set_fixmap_io uses __set_fixmap instead
    > of __set_fixmap_offset. A fix is to introduce a set_fixmap_offset_io that
    > uses the latter, and to remove the superflous call to fix_to_virt
    > (which only returns the value that set_fixmap_io has already given us).
    >
    > With this applied, my VMs are back in business. Tested on a Cortex-A57
    > platform with kvmtool as platform emulation.
    >
    > Cc: Mark Salter <msalter@redhat.com>
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Will Deacon <will.deacon@arm.com>
    > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
    > ---
    > arch/arm64/kernel/early_printk.c | 6 ++----
    > include/asm-generic/fixmap.h | 3 +++
    > 2 files changed, 5 insertions(+), 4 deletions(-)

    This will be fixed already in 3.16 with my earlycon series[1] if this
    is not taken for 3.15.

    Probably still a good addition for fixmap.

    Rob

    [1] https://lkml.org/lkml/2014/4/18/573


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