linux-kernel - Re: [PATCH 2/4] x86/boot: replace __PHYSICAL_START with LOAD_PHYSICAL

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Date: Thu, 14 Mar 2024 10:25:53 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/boot: replace __PHYSICAL_START with
 LOAD_PHYSICAL_ADDR


* Wei Yang <richard.weiyang@...il.com> wrote:

> On Wed, Mar 13, 2024 at 11:29:33AM +0100, Ingo Molnar wrote:
> >
> >* Wei Yang <richard.weiyang@...il.com> wrote:
> >
> >> Both __PHYSICAL_START and LOAD_PHYSICAL_ADDR are defined to get aligned
> >> CONFIG_PHYSICAL_START, so we can replace __PHYSICAL_START with
> >> LOAD_PHYSICAL_ADDR. And then remove the definition of __PHYSICAL_START,
> >> which is only used to define __START_KERNEL.
> >> 
> >> Since <asm/boot.h> includes <asm/pgtable_types.h>, which includes
> >> <asm/page_types.h>, it is fine to move definition from <asm/boot.h> to
> >> <asm/page_types.h>.
> >> 
> >> Signed-off-by: Wei Yang <richard.weiyang@...il.com>
> >> ---
> >>  arch/x86/include/asm/boot.h       | 5 -----
> >>  arch/x86/include/asm/page_types.h | 8 +++++---
> >>  2 files changed, 5 insertions(+), 8 deletions(-)
> >> 
> >> diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
> >> index a38cc0afc90a..12cbc57d0128 100644
> >> --- a/arch/x86/include/asm/boot.h
> >> +++ b/arch/x86/include/asm/boot.h
> >> @@ -6,11 +6,6 @@
> >>  #include <asm/pgtable_types.h>
> >>  #include <uapi/asm/boot.h>
> >>  
> >> -/* Physical address where kernel should be loaded. */
> >> -#define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \
> >> -				+ (CONFIG_PHYSICAL_ALIGN - 1)) \
> >> -				& ~(CONFIG_PHYSICAL_ALIGN - 1))
> >> -
> >>  /* Minimum kernel alignment, as a power of two */
> >>  #ifdef CONFIG_X86_64
> >>  # define MIN_KERNEL_ALIGN_LG2	PMD_SHIFT
> >> diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
> >> index 86bd4311daf8..acc1620fd121 100644
> >> --- a/arch/x86/include/asm/page_types.h
> >> +++ b/arch/x86/include/asm/page_types.h
> >> @@ -31,10 +31,12 @@
> >>  
> >>  #define VM_DATA_DEFAULT_FLAGS	VM_DATA_FLAGS_TSK_EXEC
> >>  
> >> -#define __PHYSICAL_START	ALIGN(CONFIG_PHYSICAL_START, \
> >> -				      CONFIG_PHYSICAL_ALIGN)
> >> +/* Physical address where kernel should be loaded. */
> >> +#define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \
> >> +				+ (CONFIG_PHYSICAL_ALIGN - 1)) \
> >> +				& ~(CONFIG_PHYSICAL_ALIGN - 1))
> >
> >I agree with this simplification, but the ALIGN() expression is far easier 
> >to read, so please keep that one instead of the open-coded version.
> >
> 
> I just tried to define LOAD_PHYSICAL_ADDR by ALIGN, but face a compile error
> on compressed/head_[32|64].o.
> 
> $ make arch/x86/boot/compressed/head_64.o
>   CALL    scripts/checksyscalls.sh
>   DESCEND objtool
>   INSTALL libsubcmd_headers
>   AS      arch/x86/boot/compressed/head_64.o
> arch/x86/boot/compressed/head_64.S: Assembler messages:
> arch/x86/boot/compressed/head_64.S:154: Error: junk (0x1000000,0x200000)' after expression
> arch/x86/boot/compressed/head_64.S:154: Error: number of operands mismatch for 16' after expression
> arch/x86/boot/compressed/head_64.S:157: Error: junk mov'
> arch/x86/boot/compressed/head_64.S:330: Error: junk (0x1000000,0x200000)' after expression
> arch/x86/boot/compressed/head_64.S:330: Error: number of operands mismatch for 16' after expression
> arch/x86/boot/compressed/head_64.S:333: Error: junk movq'
> 
> If my understanding is correct, the reason is linkage.h defines ALIGN, which
> is ".balign xxx". Maybe this is why original LOAD_PHYSICAL_ADDR doesn't use
> ALIGN.

linkage.h defines __ALIGN, which is different from ALIGN().

Also, a number of .S files seem to be using some sort of ALIGN() method 
within arch/x86/, according to:

   git grep 'ALIGN(' -- 'arch/x86/*.S'

> So is this ok to keep the open-coded definition?

It would be nice to figure out why ALIGN() appears to be working in other 
cases in .S files, while not in this case.

Thanks,

	Ingo