From: Jan Beulich <jbeulich@suse.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>
Subject: Re: [Xen-devel] [PATCH v2 2/6] x86/boot: Only jump into low trampoline code for real-mode boot
Date: Mon, 12 Aug 2019 11:10:35 +0200 [thread overview]
Message-ID: <7ba6171d-b3a1-14e8-184b-634c5415fe35@suse.com> (raw)
In-Reply-To: <6dc2b63127f966961aeb2a7bfe89a5cdce83241b.camel@infradead.org>
On 09.08.2019 17:01, David Woodhouse wrote:
> --- a/xen/arch/x86/boot/head.S
> +++ b/xen/arch/x86/boot/head.S
> @@ -735,7 +735,17 @@ trampoline_setup:
> /* Switch to low-memory stack which lives at the end of trampoline region. */
> mov sym_fs(trampoline_phys),%edi
> lea TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
> + cmpb $0, sym_fs(skip_realmode)
> + jz 1f
> + /* If no-real-mode, jump straight to trampoline_protmode_entry */
> + lea trampoline_protmode_entry-trampoline_start(%edi),%eax
> + /* EBX == 0 indicates we are the BP (Boot Processor). */
> + xor %ebx,%ebx
> + jmp 2f
> +1:
> + /* Go via 16-bit code in trampoline_boot_cpu_entry */
> lea trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
> +2:
> pushl $BOOT_CS32
> push %eax
May I suggest to slightly streamline this into
/* Switch to low-memory stack which lives at the end of trampoline region. */
mov sym_fs(trampoline_phys),%edi
lea TRAMPOLINE_SPACE+TRAMPOLINE_STACK_SPACE(%edi),%esp
/* Go via 16-bit code in trampoline_boot_cpu_entry */
lea trampoline_boot_cpu_entry-trampoline_start(%edi),%eax
cmpb $0,sym_fs(skip_realmode)
je 1f
/* If no-real-mode, jump straight to trampoline_protmode_entry */
lea trampoline_protmode_entry-trampoline_start(%edi),%eax
/* EBX == 0 indicates we are the BP (Boot Processor). */
xor %ebx,%ebx
1:
pushl $BOOT_CS32
push %eax
perhaps with the second slightly adapted to it now being an override
rather than an alternative path?
Additionally I think it would be nice if the clearing of %ebx wasn't
replicated here and ...
> --- a/xen/arch/x86/boot/trampoline.S
> +++ b/xen/arch/x86/boot/trampoline.S
> @@ -194,9 +194,6 @@ gdt_48: .word 6*8-1
>
> .code32
> trampoline_boot_cpu_entry:
> - cmpb $0,bootsym_rel(skip_realmode,5)
> - jnz .Lskip_realmode
> -
> /* Load pseudo-real-mode segments. */
> mov $BOOT_PSEUDORM_DS,%eax
> mov %eax,%ds
> @@ -276,7 +273,6 @@ trampoline_boot_cpu_entry:
> mov %eax,%gs
> mov %eax,%ss
>
> -.Lskip_realmode:
> /* EBX == 0 indicates we are the BP (Boot Processor). */
> xor %ebx,%ebx
... here. Why don't you further do
.code32
trampoline_protmode_entry_bsp:
/* EBX == 0 indicates we are the BSP (Boot Strap Processor). */
xor %ebx,%ebx
trampoline_protmode_entry:
directing the BSP paths to the new label?
Jan
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next prev parent reply other threads:[~2019-08-12 9:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1565362089.git.dwmw@amazon.co.uk>
2019-08-09 15:01 ` [Xen-devel] [PATCH v2 1/6] x86/boot: Remove gratuitous call back into low-memory code David Woodhouse
2019-08-09 15:01 ` [Xen-devel] [PATCH v2 2/6] x86/boot: Only jump into low trampoline code for real-mode boot David Woodhouse
2019-08-12 9:10 ` Jan Beulich [this message]
2019-08-21 14:04 ` David Woodhouse
2019-08-27 8:43 ` Jan Beulich
2019-08-09 15:01 ` [Xen-devel] [PATCH v2 3/6] x86/boot: Split bootsym() into four types of relocations David Woodhouse
2019-08-12 9:41 ` Jan Beulich
2019-08-19 15:24 ` David Woodhouse
2019-08-09 15:02 ` [Xen-devel] [PATCH v2 4/6] x86/boot: Rename trampoline_{start, end} to boot_trampoline_{start, end} David Woodhouse
2019-08-12 9:55 ` Jan Beulich
2019-08-19 15:24 ` David Woodhouse
2019-08-27 8:51 ` Jan Beulich
2019-08-27 9:31 ` David Woodhouse
2019-08-09 15:02 ` [Xen-devel] [PATCH v2 5/6] x86/boot: Copy 16-bit boot variables back up to Xen image David Woodhouse
2019-08-12 10:24 ` Jan Beulich
2019-08-19 15:25 ` David Woodhouse
2019-08-27 8:59 ` Jan Beulich
2019-08-27 9:19 ` David Woodhouse
2019-08-09 15:02 ` [Xen-devel] [PATCH v2 6/6] x86/boot: Do not use trampoline for no-real-mode boot paths David Woodhouse
2019-08-12 10:55 ` Jan Beulich
2019-08-19 15:25 ` David Woodhouse
2019-08-27 9:07 ` Jan Beulich
2019-08-27 9:12 ` David Woodhouse
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