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SubjectRe: [PATCH v2 11/15] arm64: add EFI stub
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On Wed, 2014-03-19 at 10:57 +0000, Catalin Marinas wrote:
> On Tue, Mar 18, 2014 at 09:40:31PM +0000, Mark Salter wrote:
> > On Tue, 2014-03-18 at 18:28 +0000, Catalin Marinas wrote:
> > > If UEFI doesn't handle the caches, the only thing left to EFI_STUB is to
> > > flush by MVA. We don't need to flush the whole DRAM (and I would even
> > > recommend it) but at least the relevant kernel code/data touched with
> > > the MMU disabled.
> >
> > So, it goes like this:
> >
> > 1) UEFI calls stub with MMU/Caches on. Stub/kernel can be anywhere.
> > 2) Stub runs and relocates kernel to the desired runtime location
> > but continues to execute from wherever UEFI loaded it until just
> > after ExitBootServices().
> > 3) After ExitBootServices, efi_entry() returns relocated entry point
> > for kernel to efi_stub_entry() in efi-entry.S where the Dcache and
> > MMU are turned off, the __flush_dcache_all is called, then the
> > code jumps to the kernel proper entry point.
> >
> > It isn't clear to me if UEFI does cache flushing at ExitBootServices
> > time, but even so, at least stack use will get cached between then and
> > the kernel entry point. The stub could conceivably get its hands on the
> > EFI memmap and invalidate dcache using address ranges from UEFI memory
> > descriptors so maybe that is the way we should do it.
>
> I think the stub just needs to flush the relocated kernel image, ensure
> it is sync with the memory. Additional flushing can be done by the
> kernel for bits it writes (like page tables, code patching etc). We can
> enter the kernel with the SCTLR.I bit set, so it can allocate in an
> unified cache already and D-cache maintenance would be needed anyway.

How about this?

diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
index 83bfb72..ed480b2 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -52,11 +52,19 @@ ENTRY(efi_stub_entry)
* efi_entry() will have relocated the kernel image if necessary
* and we return here with device tree address in x0 and the kernel
* entry point stored at *image_addr. Save those values in registers
- * which are preserved by __flush_dcache_all.
+ * which are callee preserved.
*/
- ldr x1, [sp, #16]
mov x20, x0
- mov x21, x1
+ ldr x0, [sp, #16]
+ mov x21, x0
+
+ adrp x1, _text
+ add x1, x1, #:lo12:_text
+ adrp x2, _edata
+ add x2, x2, #:lo12:_edata
+ sub x1, x2, x1
+
+ bl __flush_dcache_area

/* Turn off Dcache and MMU */
mrs x0, CurrentEL
@@ -76,8 +84,6 @@ ENTRY(efi_stub_entry)
msr sctlr_el1, x0
isb
2:
- bl __flush_dcache_all
-
/* Jump to real entry point */
mov x0, x20
mov x1, xzr




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