On 07/23/2014 12:59 PM, Ard Biesheuvel wrote:
> On 23 July 2014 11:34, Mark Rutland <mark.rutland@xxxxxxx> wrote:
>> Hi Ard,
>>
>> This is certainly a neat feature, and I definitely want to be able to
>> boot BE kernels via UEFI.
>>
>
> Good!
>
>> However, I'm wary of calling EFI in a physical (i.e. idmap with dcaches
>> off) context. I'm not sure anyone else does that, and I'm not sure
>> whether that's going to work (both because of the cache maintenance
>> requirements and the expectations of a given UEFI implementation w.r.t.
>> memory cacheability).
>>
>
> I have developed an alternate version in the mean time that switches
> to a LE idmap (so with D-cache enabled), but this is an imperfect
> solution as well, as (like in the MMU off case), the vector base
> virtual address cannot be resolved when the EE bit is cleared (as
> TTBR1 points to a BE page table) so any exception taken locks the
> machine hard. I am not sure if this can be solved in any way other
> than changing exception levels. Or install an alternate vector table
> for the duration of the runtime services call that flips the EE bit
> back, restores VBAR to its original address, and jumps into it. None
> of this is very sexy, though ...
>
>> I'd hoped we'd be able to use a LE EL0 context to call the runtime
>> services in, but I'm not sure that's possible by the spec :(
>>
>
> Nope, they should be called at the exception level UEFI was started in
> (as Leif tells me)
>
>> As I understand it, we shouldn't need these runtime services to simply
>> boot a BE kernel.
>>
>
> Well, the significance of the variable store related Runtime Services
> is that they are used by an installer (through efibootmgr) to program
> the kernel command line. Hence the choice for just these services in
> the minimal implementation.
>
The below patch is an alternate approach with a LE id mapping in
efi_pg_dir. (Patch that sets it up omitted).
This dodges all the concerns related to caching, hopefully, as the LE id
mapping and the BE id mapping in idmap_pg_dir should agree on the memory
attributes of all common mappings.
This also addresses the FIQ and exception concerns, although I fully
realise that this is likely too controversial. Suggestions for less
controversial approaches are highly appreciated. As said, booting a BE
kernel is useful by itself, but without being able to use efibootmgr it
is a bit crippled.
--
Ard.
diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index a34fd3b12e2b..2eeae5ae55b2 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -44,4 +44,6 @@ extern void efi_idmap_init(void);
#define efi_call_early(f, ...) sys_table_arg->boottime->f(__VA_ARGS__)
+extern int efi_be_runtime_setup(void);
+
#endif /* _ASM_EFI_H */
diff --git a/arch/arm64/kernel/efi-be-call.S
b/arch/arm64/kernel/efi-be-call.S
new file mode 100644
index 000000000000..8da53a225fab
--- /dev/null
+++ b/arch/arm64/kernel/efi-be-call.S
@@ -0,0 +1,129 @@
+
+#include <linux/linkage.h>
+
+ .macro flush_tlb_all
+ dsb ishst
+ tlbi vmalle1is
+ dsb ish
+ isb
+ .endm
+
+ .text
+ /*
+ * Alternate vector table so we can trap exceptions while in LE mode
+ * and make the world sane again before letting the kernel handle the
+ * exception as usual. Clobbers x30.
+ */
+ .align 12
+.Lvectors:
+ .irpc i, 0123456789abcdef
+ .align 7
+ /* switch back to BE and temporarily disable MMU */
+ mrs x30, sctlr_el1
+ bic x30, x30, #1 << 0 // clear SCTLR.M
+ orr x30, x30, #1 << 25 // set SCTLR.EE
+ msr sctlr_el1, x30
+ isb
+
+ /* needed as TLBs are permitted to cache the EE bit */
+ flush_tlb_all
+
+ /* re-install BE idmap */
+ adrp x30, idmap_pg_dir
+ msr ttbr0_el1, x30
+ mrs x30, sctlr_el1
+ orr x30, x30, #1 << 0 // set SCTLR.M
+ msr sctlr_el1, x30 // re-enable MMU
+ isb
+
+ /*
+ * Use the virtual and physical addresses of 'vectors' to restore the
+ * virtual offset of sp.
+ */
+ adrp x30, vectors
+ add x30, x30, #:lo12:vectors
+ sub sp, sp, x30
+ ldr x30, =vectors
+ add sp, sp, x30
+
+ /* reinstall vector table */
+ msr vbar_el1, x30 // restore VBAR to 'vectors'
+ isb
+
+ add x30, x30, #(0x\i * 0x80) // jump to real vector
+ ret
+ .endr
+
+ENTRY(efi_be_phys_call)
+ /*
+ * Entered at physical address with 1:1 mapping enabled and interrupts
+ * disabled.
+ */
+ stp x29, x30, [sp, #-48]!
+ mov x29, sp
+ stp x25, x26, [sp, #16]
+ stp x27, x28, [sp, #32]
+
+ ldr x8, =efi_be_phys_call // virt address of this function
+ adr x9, efi_be_phys_call // phys address of this function
+ sub x9, x8, x9 // calculate virt to phys offset in x9
+
+ /* get phys address of stack */
+ sub sp, sp, x9
+
+ /* mask FIQs */
+ mrs x25, daif
+ msr daifset, #8
+
+ /* install alternate vector table */
+ mrs x28, vbar_el1
+ adrp x8, .Lvectors
+ msr vbar_el1, x8
+
+ /* switch to LE and temporarily disable MMU */
+ mrs x27, sctlr_el1
+ bic x8, x27, #1 << 25 // clear SCTLR.EE
+ bic x9, x8, #1 << 0 // clear SCTLR.M
+ msr sctlr_el1, x9
+ isb
+
+ /* needed as TLBs are permitted to cache the EE bit */
+ flush_tlb_all
+
+ /* install LE idmap */
+ adrp x9, efi_pg_dir
+ msr ttbr0_el1, x9
+ msr sctlr_el1, x8 // re-enable MMU
+ isb
+
+ /* restore inputs but rotated by 1 register */
+ mov x6, x0
+ mov x0, x1
+ mov x1, x2
+ mov x2, x3
+ mov x3, x4
+ mov x4, x5
+ blr x6
+
+ /* switch back to BE and temporarily disable MMU */
+ bic x9, x27, #1 << 0 // clear SCTLR.M
+ msr sctlr_el1, x9
+ isb
+
+ /* needed as TLBs are permitted to cache the EE bit */
+ flush_tlb_all
+
+ /* re-install BE idmap */
+ adrp x8, idmap_pg_dir
+ msr ttbr0_el1, x8
+ msr sctlr_el1, x27 // re-enable MMU
+ msr vbar_el1, x28 // restore VBAR
+ msr daif, x25
+ isb
+
+ mov sp, x29
+ ldp x25, x26, [sp, #16]
+ ldp x27, x28, [sp, #32]
+ ldp x29, x30, [sp], #48
+ ret
+ENDPROC(efi_be_phys_call)
diff --git a/arch/arm64/kernel/efi-be-runtime.c
b/arch/arm64/kernel/efi-be-runtime.c
new file mode 100644
index 000000000000..abcc275481bd
--- /dev/null
+++ b/arch/arm64/kernel/efi-be-runtime.c
@@ -0,0 +1,105 @@
+
+#include <linux/efi.h>
+#include <linux/spinlock.h>
+#include <asm/efi.h>
+#include <asm/neon.h>
+#include <asm/tlbflush.h>
+
+static efi_runtime_services_t *runtime;
+static efi_status_t (*efi_be_call)(phys_addr_t func, ...);
+
+static DEFINE_SPINLOCK(efi_be_rt_lock);
+
+static unsigned long efi_be_call_pre(void)
+{
+ unsigned long flags;
+
+ kernel_neon_begin();
+ spin_lock_irqsave(&efi_be_rt_lock, flags);
+ cpu_switch_mm(idmap_pg_dir, &init_mm);
+ flush_tlb_all();
+ return flags;
+}
+
+static void efi_be_call_post(unsigned long flags)
+{
+ cpu_switch_mm(current, current->active_mm);
+ flush_tlb_all();
+ spin_unlock_irqrestore(&efi_be_rt_lock, flags);
+ kernel_neon_end();
+}
+
+static efi_status_t efi_be_get_variable(efi_char16_t *name,
+ efi_guid_t *vendor,
+ u32 *attr,
+ unsigned long *data_size,
+ void *data)
+{
+ unsigned long flags;
+ efi_status_t status;
+
+ *data_size = cpu_to_le64(*data_size);
+ flags = efi_be_call_pre();
+ status = efi_be_call(le64_to_cpu(runtime->get_variable),
+ virt_to_phys(name), virt_to_phys(vendor),
+ virt_to_phys(attr), virt_to_phys(data_size),
+ virt_to_phys(data));
+ efi_be_call_post(flags);
+ *attr = le32_to_cpu(*attr);
+ *data_size = le64_to_cpu(*data_size);
+ return status;
+}
+
+static efi_status_t efi_be_get_next_variable(unsigned long *name_size,
+ efi_char16_t *name,
+ efi_guid_t *vendor)
+{
+ unsigned long flags;
+ efi_status_t status;
+
+ *name_size = cpu_to_le64(*name_size);
+ flags = efi_be_call_pre();
+ status = efi_be_call(le64_to_cpu(runtime->get_next_variable),
+ virt_to_phys(name_size), virt_to_phys(name),
+ virt_to_phys(vendor));
+ efi_be_call_post(flags);
+ *name_size = le64_to_cpu(*name_size);
+ return status;
+}
+
+static efi_status_t efi_be_set_variable(efi_char16_t *name,
+ efi_guid_t *vendor,
+ u32 attr,
+ unsigned long data_size,
+ void *data)
+{
+ unsigned long flags;
+ efi_status_t status;
+
+ flags = efi_be_call_pre();
+ status = efi_be_call(le64_to_cpu(runtime->set_variable),
+ virt_to_phys(name), virt_to_phys(vendor),
+ attr, data_size, virt_to_phys(data));
+ efi_be_call_post(flags);
+ return status;
+}
+
+int efi_be_runtime_setup(void)
+{
+ extern u8 efi_be_phys_call[];
+
+ runtime = ioremap_cache(le64_to_cpu(efi.systab->runtime),
+ sizeof(efi_runtime_services_t));
+ if (!runtime) {
+ pr_err("Failed to set up BE wrappers for UEFI Runtime Services!\n");
+ return -EFAULT;
+ }
+
+ efi_be_call = (void *)virt_to_phys(efi_be_phys_call);
+
+ efi.get_variable = efi_be_get_variable;
+ efi.get_next_variable = efi_be_get_next_variable;
+ efi.set_variable = efi_be_set_variable;
+
+ return 0;
+}
diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index c65c6a50395d..3f28854e96a9 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -426,6 +426,20 @@ static int __init arm64_enter_virtual_mode(void)
efi.memmap = &memmap;
+ if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN)) {
+ efi.systab = ioremap_cache(efi_system_table,
+ sizeof(efi_system_table_t));
+ if (!efi.systab) {
+ pr_err("Failed to remap EFI system table!\n");
+ return -1;
+ }
+ free_boot_services();
+ set_bit(EFI_SYSTEM_TABLES, &efi.flags);
+ if (efi_be_runtime_setup() == 0)
+ set_bit(EFI_RUNTIME_SERVICES, &efi.flags);
+ return 0;
+ }
+
/* Map the runtime regions */
virtmap = kmalloc(mapsize, GFP_KERNEL);
if (!virtmap) {
--
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