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    Subject[PATCHv3 3/4] efi: Add a function to look up existing IO memory mappings
    The EFI initialization creates virtual mappings for EFI boot services
    memory, so if a driver wants to access EFI boot services memory, it
    cannot call ioremap itself; doing so will trip the WARN about mapping
    RAM twice. Thus, a driver accessing EFI boot services memory must do so
    via the existing mapping already created during EFI intiialization.
    Since the EFI code already maintains a memory map for that memory, add a
    function efi_lookup_mapped_addr to look up mappings in that memory map.

    Signed-off-by: Josh Triplett <josh@joshtriplett.org>
    ---
    arch/x86/platform/efi/efi.c | 28 ++++++++++++++++++++++++++++
    include/linux/efi.h | 1 +
    2 files changed, 29 insertions(+)

    diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
    index ab2cfe8..90023d1 100644
    --- a/arch/x86/platform/efi/efi.c
    +++ b/arch/x86/platform/efi/efi.c
    @@ -777,6 +777,34 @@ static void __init runtime_code_page_mkexec(void)
    }

    /*
    + * We can't ioremap data in EFI boot services RAM, because we've already mapped
    + * it as RAM. So, look it up in the existing EFI memory map instead. Only
    + * callable after efi_enter_virtual_mode and before efi_free_boot_services.
    + */
    +void __iomem *efi_lookup_mapped_addr(u64 phys_addr)
    +{
    + void *p;
    + if (WARN_ON(!memmap.map))
    + return NULL;
    + for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
    + efi_memory_desc_t *md = p;
    + u64 size = md->num_pages << EFI_PAGE_SHIFT;
    + u64 end = md->phys_addr + size;
    + if (!(md->attribute & EFI_MEMORY_RUNTIME) &&
    + md->type != EFI_BOOT_SERVICES_CODE &&
    + md->type != EFI_BOOT_SERVICES_DATA)
    + continue;
    + if (!md->virt_addr)
    + continue;
    + if (phys_addr >= md->phys_addr && phys_addr < end) {
    + phys_addr += md->virt_addr - md->phys_addr;
    + return (__force void __iomem *)phys_addr;
    + }
    + }
    + return NULL;
    +}
    +
    +/*
    * This function will switch the EFI runtime services to virtual mode.
    * Essentially, look through the EFI memmap and map every region that
    * has the runtime attribute bit set in its memory descriptor and update
    diff --git a/include/linux/efi.h b/include/linux/efi.h
    index 3c72c27..00aa5de 100644
    --- a/include/linux/efi.h
    +++ b/include/linux/efi.h
    @@ -502,6 +502,7 @@ extern void efi_free_boot_services(void);
    static void efi_enter_virtual_mode(void) {}
    static void efi_free_boot_services(void) {}
    #endif
    +extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
    extern u64 efi_get_iobase (void);
    extern u32 efi_mem_type (unsigned long phys_addr);
    extern u64 efi_mem_attributes (unsigned long phys_addr);
    --
    1.7.10.4


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