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    SubjectRe: [PATCH][EFI] Run EFI in physical mode
    Takao Indoh <indou.takao@jp.fujitsu.com> writes:

    > Hi all,
    >
    > The attached patch enables EFI to run in physical mode.
    >
    > Basically EFI is in physical mode at first and it's switched to virtual
    > mode after calling SetVirtualAddressMap. By applying this patch, you can
    > run EFI always in physical mode. And you can also specify "virtefi" as
    > kernel boot parameter to run EFI in virtual mode as before. Note that
    > this patch supports only x86_64.
    >
    > This is needed to run kexec/kdump in EFI-booted system. The following is
    > an original discussion. In this thread, I explained that kdump does not
    > work because EFI system table is modified by SetVirtualAddressMap. And
    > the idea to run EFI in physical mode was proposed. This patch implements
    > it.
    >
    > http://marc.info/?l=linux-kernel&m=128018221820234&w=2
    >> When the 1st kernel boots, EFI system table(efi_system_table_t) is
    >> modified by SetVirtualAddressMap, which is one of EFI runtime service.
    >> This runtime changes physical address in EFI system table to virtual
    >> address.
    >>
    >> When the 2nd kernel boots, it also receives the same EFI system table,
    >> and the address included in it is already virtual address(1st kernel
    >> rewrote it). But 2nd kernel does not know that, 2nd kernel thinks it is
    >> a physical address. This causes problems.
    >
    > Basic idea of this patch is to create EFI own pagetable. This pagetable
    > maps physical address of EFI runtime to the virtual address which is the
    > same value so that we can call it directly. For example, physical
    > address 0x800000 is mapped to virtual address 0x800000. Before calling
    > EFI runtime, cr3 register is switched to this pagetable, and restored
    > when we come back from EFI.
    >
    > Any comments would be appreciated.
    >
    > Signed-off-by: Takao Indoh <indou.takao@jp.fujitsu.com>

    Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>

    There is what appears to be unneeded redundancy (we need two
    implementations of physciall calls into efi?), but that is confined to
    the weird efi state.

    It is a shame you haven't done the little bit extra to get
    efi_pagetable_init working on x86_32.

    Overall this seems sane and confined to the x86 efi, and it looks
    like further improvements could easily be layered on top of this one.

    Eric


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