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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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