linux-kernel - Re: [PATCH RFC 1/7] x86/head/64: Mark startup_gdt and startup_gdt_descr as _

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Date:   Tue, 17 Oct 2023 15:23:11 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     <linux-kernel@...r.kernel.org>,
        "Lai Jiangshan" <jiangshan.ljs@...group.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" 
        <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        "Josh Poimboeuf" <jpoimboe@...nel.org>,
        "Anshuman Khandual" <anshuman.khandual@....com>,
        "Mike Rapoport" <rppt@...nel.org>,
        "Pasha Tatashin" <pasha.tatashin@...een.com>
Subject: Re: [PATCH RFC 1/7] x86/head/64: Mark startup_gdt and
 startup_gdt_descr as __initdata

On Mon, Oct 16, 2023 at 07:57:06PM +0800, Ingo Molnar wrote:
> 
> * Hou Wenlong <houwenlong.hwl@...group.com> wrote:
> 
> > As startup_gdt and startup_gdt_descr are only used in booting, make them
> > as __initdata to allow them to be freed after boot.
> > 
> > Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> > ---
> >  arch/x86/kernel/head64.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> > index 49f7629b17f7..dd357807ffb5 100644
> > --- a/arch/x86/kernel/head64.c
> > +++ b/arch/x86/kernel/head64.c
> > @@ -69,7 +69,7 @@ EXPORT_SYMBOL(vmemmap_base);
> >  /*
> >   * GDT used on the boot CPU before switching to virtual addresses.
> >   */
> > -static struct desc_struct startup_gdt[GDT_ENTRIES] = {
> > +static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
> >  	[GDT_ENTRY_KERNEL32_CS]         = GDT_ENTRY_INIT(0xc09b, 0, 0xfffff),
> >  	[GDT_ENTRY_KERNEL_CS]           = GDT_ENTRY_INIT(0xa09b, 0, 0xfffff),
> >  	[GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(0xc093, 0, 0xfffff),
> > @@ -79,7 +79,7 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = {
> >   * Address needs to be set at runtime because it references the startup_gdt
> >   * while the kernel still uses a direct mapping.
> >   */
> > -static struct desc_ptr startup_gdt_descr = {
> > +static struct desc_ptr startup_gdt_descr __initdata = {
> >  	.size = sizeof(startup_gdt),
> >  	.address = 0,
> 
> Yeah, so I think this and patch #1 are independently useful of the PIE 
> feature, and I merged them into tip:x86/boot for a v6.7 merge.
> 
> Mind re-sending any other patches for x86 that can be merged? For example 
> patch #6 looks good too, but was mixed up a bit with a previous 
> PIE-enablement patch. Moving the __head definition to a header should also 
> probably done as a separate patch, followed by the widening of its use.
>
Hi Ingo,

I have sent patch #6 separately for x86. Do you have any ideas about
building the head code as PIE? Should I resend the patchset for the PIE
feature?

Thanks!

> Thanks,
> 
> 	Ingo