| Message ID | 1395241998.2967.52.camel@deneb.redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Mar 19, 2014 at 03:13:18PM +0000, Mark Salter wrote: > 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 BTW, some comments to make it easier to review the code later about what's at [sp, #16]. > + > + adrp x1, _text > + add x1, x1, #:lo12:_text > + adrp x2, _edata > + add x2, x2, #:lo12:_edata > + sub x1, x2, x1 > + > + bl __flush_dcache_area Looks fine. We also need a "ic ialluis", is any other part of EFI_STUB invalidating the I-cache? We need a patch to invalidate the D-cache for areas of memory that the kernel touches but I'll do this as a separate patch.
On Wed, 2014-03-19 at 16:01 +0000, Catalin Marinas wrote: > On Wed, Mar 19, 2014 at 03:13:18PM +0000, Mark Salter wrote: > > 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 > > BTW, some comments to make it easier to review the code later about > what's at [sp, #16]. Okay. > > > + > > + adrp x1, _text > > + add x1, x1, #:lo12:_text > > + adrp x2, _edata > > + add x2, x2, #:lo12:_edata > > + sub x1, x2, x1 > > + > > + bl __flush_dcache_area > > Looks fine. We also need a "ic ialluis", is any other part of EFI_STUB > invalidating the I-cache? No. I will add it.
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