From: Baoquan He <bhe@redhat.com>
To: John Sperbeck <jsperbeck@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
Eric Biederman <ebiederm@xmission.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
kexec@lists.infradead.org,
Dave Hansen <dave.hansen@linux.intel.com>,
Zac Tang <zactang@google.com>, Cloud Hsu <cloudhsu@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/kexec: set MIN_KERNEL_LOAD_ADDR to 0x01000000
Date: Tue, 14 Nov 2023 22:16:01 +0800 [thread overview]
Message-ID: <ZVOBIfIpuTIO+E8M@MiWiFi-R3L-srv> (raw)
In-Reply-To: <CAFNjLiVAdcPEc+UK_5Z+uutqAVki5geWgpWewzu9iyJsYyiRjw@mail.gmail.com>
Hi John,
On 10/23/23 at 02:54pm, John Sperbeck wrote:
> On Sun, Oct 22, 2023 at 7:42 PM H. Peter Anvin <hpa@zytor.com> wrote:
......
> > >---
> > > arch/x86/kernel/kexec-bzimage64.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > >diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
> > >index a61c12c01270..d6bf6c13dab1 100644
> > >--- a/arch/x86/kernel/kexec-bzimage64.c
> > >+++ b/arch/x86/kernel/kexec-bzimage64.c
> > >@@ -36,7 +36,7 @@
> > > */
> > > #define MIN_PURGATORY_ADDR 0x3000
> > > #define MIN_BOOTPARAM_ADDR 0x3000
> > >-#define MIN_KERNEL_LOAD_ADDR 0x100000
> > >+#define MIN_KERNEL_LOAD_ADDR 0x1000000
> > > #define MIN_INITRD_LOAD_ADDR 0x1000000
> > >
> > > /*
> >
> > This doesn't make any sense to me. There is already a high water mark for his much memory the kernel needs until an initrd or setup_data item can appear. This is just a hack, please fix it properly.
>
> The startup_64() code in head_64.S changes behavior based on whether
> it's running below or above LOAD_PHYSICAL_ADDR:
>
> #ifdef CONFIG_RELOCATABLE
> leaq startup_32(%rip) /* - $startup_32 */, %rbp
> movl BP_kernel_alignment(%rsi), %eax
> decl %eax
> addq %rax, %rbp
> notq %rax
> andq %rax, %rbp
> cmpq $LOAD_PHYSICAL_ADDR, %rbp
> jae 1f
> #endif
> movq $LOAD_PHYSICAL_ADDR, %rbp
> 1:
>
> In my example, we were running from address 0x00400000. The %rbp
> register will start with 0x00400000, but will be changed to 0x01000000
> after the check against LOAD_PHYSICAL_ADDR fails.
>
> The 0x01000000 value in %rbp is passed to extract_kernel as the
> 'output' argument. Unless choose_random_location() decides
> differently, this will be where the kernel is decompressed to. The
> size of the kernel is large enough in my example that the
> decompression overruns the initrd.
>
> If the startup_64() code didn't have the LOAD_PHYSICAL_ADDR check and
> used %rpb as is, then there would be no issue. The decompression
> would have been to 0x00400000 and would have completed before reaching
> the initrd memory.
>
> That is, the kexec code is being careful to ensure that the kernel and
> initrd memory doesn't overlap, but isn't paying attention to what
> happens if the kernel memory is below LOAD_PHYSICAL_ADDR (the kernel
> address is effectively changed to a different location). My proposed
> change makes it aware, and avoids such addresses.
Wondering why kexec-ed kernel is located under 0x1000000. The loading
code will search physical memory regions bottom up for an available one.
Usually, kexec kernel will be loaded above 16M.
I have posted a patchset to load kernel at top of system RAM for kexec_file
load just as kexec_load has been doing. Do you think it's helpful?
[PATCH 0/2] kexec_file: Load kernel at top of system RAM if required
https://lore.kernel.org/all/20231114091658.228030-1-bhe@redhat.com/T/#u
Thanks
Baoquan
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prev parent reply other threads:[~2023-11-14 14:16 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-23 2:31 [PATCH] x86/kexec: set MIN_KERNEL_LOAD_ADDR to 0x01000000 John Sperbeck
2023-10-23 2:41 ` H. Peter Anvin
2023-10-23 21:54 ` John Sperbeck
2023-11-14 14:16 ` Baoquan He [this message]
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