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Date: Tue, 18 Mar 2014 14:48:30 -0700 From: Roy Franz <roy.franz@...aro.org> To: Mark Salter <msalter@...hat.com> Cc: Catalin Marinas <catalin.marinas@....com>, Leif Lindholm <leif.lindholm@...aro.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>, "matt.fleming@...el.com" <matt.fleming@...el.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org> Subject: Re: [PATCH v2 11/15] arm64: add EFI stub On Tue, Mar 18, 2014 at 2:40 PM, Mark Salter <msalter@...hat.com> wrote: > On Tue, 2014-03-18 at 18:28 +0000, Catalin Marinas wrote: >> On Tue, Mar 18, 2014 at 02:40:29PM +0000, Mark Salter wrote: >> > On Tue, 2014-03-18 at 12:09 +0000, Catalin Marinas wrote: >> > > On Thu, Mar 13, 2014 at 10:47:04PM +0000, Leif Lindholm wrote: >> > > > --- /dev/null >> > > > +++ b/arch/arm64/kernel/efi-entry.S >> > > > @@ -0,0 +1,93 @@ >> > > > +/* >> > > > + * EFI entry point. >> > > > + * >> > > > + * Copyright (C) 2013 Red Hat, Inc. >> > > > + * Author: Mark Salter <msalter@...hat.com> >> > > > + * >> > > > + * This program is free software; you can redistribute it and/or modify >> > > > + * it under the terms of the GNU General Public License version 2 as >> > > > + * published by the Free Software Foundation. >> > > > + * >> > > > + */ >> > > > +#include <linux/linkage.h> >> > > > +#include <linux/init.h> >> > > > + >> > > > +#include <asm/assembler.h> >> > > > + >> > > > +#define EFI_LOAD_ERROR 0x8000000000000001 >> > > > + >> > > > + __INIT >> > > > + >> > > > + /* >> > > > + * We arrive here from the EFI boot manager with: >> > > > + * >> > > > + * * MMU on with identity-mapped RAM. >> > > > + * * Icache and Dcache on >> > > > + * >> > > > + * We will most likely be running from some place other than where >> > > > + * we want to be. The kernel image wants to be placed at TEXT_OFFSET >> > > > + * from start of RAM. >> > > > + */ >> > > > +ENTRY(efi_stub_entry) >> > > > + stp x29, x30, [sp, #-32]! >> > > > + >> > > > + /* >> > > > + * Call efi_entry to do the real work. >> > > > + * x0 and x1 are already set up by firmware. Current runtime >> > > > + * address of image is calculated and passed via *image_addr. >> > > > + * >> > > > + * unsigned long efi_entry(void *handle, >> > > > + * efi_system_table_t *sys_table, >> > > > + * unsigned long *image_addr) ; >> > > > + */ >> > > > + adrp x8, _text >> > > > + add x8, x8, #:lo12:_text >> > > > + add x2, sp, 16 >> > > > + str x8, [x2] >> > > > + bl efi_entry >> > > > + cmn x0, #1 >> > > > + b.eq efi_load_fail >> > > > + >> > > > + /* >> > > > + * 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. >> > > > + */ >> > > > + ldr x1, [sp, #16] >> > > > + mov x20, x0 >> > > > + mov x21, x1 >> > > > + >> > > > + /* Turn off Dcache and MMU */ >> > > > + mrs x0, CurrentEL >> > > > + cmp x0, #PSR_MODE_EL2t >> > > > + ccmp x0, #PSR_MODE_EL2h, #0x4, ne >> > > > + b.ne 1f >> > > > + mrs x0, sctlr_el2 >> > > > + bic x0, x0, #1 << 0 // clear SCTLR.M >> > > > + bic x0, x0, #1 << 2 // clear SCTLR.C >> > > > + msr sctlr_el2, x0 >> > > > + isb >> > > > + b 2f >> > > > +1: >> > > > + mrs x0, sctlr_el1 >> > > > + bic x0, x0, #1 << 0 // clear SCTLR.M >> > > > + bic x0, x0, #1 << 2 // clear SCTLR.C >> > > > + msr sctlr_el1, x0 >> > > > + isb >> > > > +2: >> > > > + bl __flush_dcache_all >> > > >> > > In linux-next I'm pushing a patch which no longer exports the >> > > __flush_dcache_all function. The reason is that it doesn't really work >> > > if you have a (not fully transparent) external cache like on the Applied >> > > Micro boards. There other issues when running as a guest as well. >> > > >> > > If you know exactly what needs to be flushed here, can you use a range >> > > (MVA) operation? >> > >> > This is just before the EFI stub jumps to kernel proper. The only things >> > in the dcache would be from identity mapped references to RAM used by >> > UEFI. The booting.txt doc says dcache should be off and invalidated. I >> > am just wanting to comply with that. The code here doesn't really know >> > the extent of DRAM to flush by address. >> >> Does UEFI do anything with the caches before invoking the EFI_STUB code? >> I guess it doesn't since that's just another application for it. Can >> UEFI flush the caches via exit boot? When is this called? >> >> As I said, we have a real problem here since the EFI_STUB call does not >> have information about the SoC to be able to flush all the caches. But >> UEFI should know more about the hardware. >> >> 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 looked at the UEFI spec and there is no mention of cache flushing in ExitBootServices(), so it seems it is up to the OS to do any cache management. Roy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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