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Subject[tip:x86/kdump] x86/crash: Add e820 reserved ranges to kdump kernel's e820 table
Commit-ID:  980621daf368f2b9aa69c7ea01baa654edb7577b
Gitweb: https://git.kernel.org/tip/980621daf368f2b9aa69c7ea01baa654edb7577b
Author: Lianbo Jiang <lijiang@redhat.com>
AuthorDate: Tue, 23 Apr 2019 09:30:07 +0800
Committer: Borislav Petkov <bp@suse.de>
CommitDate: Thu, 20 Jun 2019 10:05:06 +0200

x86/crash: Add e820 reserved ranges to kdump kernel's e820 table

At present, when using the kexec_file_load() syscall to load the kernel
image and initramfs, for example:

kexec -s -p xxx

the kernel does not pass the e820 reserved ranges to the second kernel,
which might cause two problems:

1. MMCONFIG: A device in PCI segment 1 cannot be discovered by the
kernel PCI probing without all the e820 I/O reservations being present
in the e820 table. Which is the case currently, because the kdump kernel
does not have those reservations because the kexec command does not pass
the I/O reservation via the "memmap=xxx" command line option.

Further details courtesy of Bjorn Helgaas¹: I think you should regard
correct MCFG/ECAM usage in the kdump kernel as a requirement. MMCONFIG
(aka ECAM) space is described in the ACPI MCFG table. If you don't have
ECAM:

(a) PCI devices won't work at all on non-x86 systems that use only
ECAM for config access,

(b) you won't be able to access devices on non-0 segments (granted,
there aren't very many of these yet, but there will be more in the
future), and

(c) you won't be able to access extended config space (addresses
0x100-0xfff), which means none of the Extended Capabilities will be
available (AER, ACS, ATS, etc).

2. The second issue is that the SME kdump kernel doesn't work without
the e820 reserved ranges. When SME is active in the kdump kernel, those
reserved regions are still decrypted, but because those reserved ranges
are not present at all in kdump kernel's e820 table, they are accessed
as encrypted. Which is obviously wrong.

[1]: https://lkml.kernel.org/r/CABhMZUUscS3jUZUSM5Y6EYJK6weo7Mjj5-EAKGvbw0qEe%2B38zw@mail.gmail.com

[ bp: Heavily massage commit message. ]

Suggested-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Baoquan He <bhe@redhat.com>
Cc: Bjorn Helgaas <bjorn.helgaas@gmail.com>
Cc: dave.hansen@linux.intel.com
Cc: Dave Young <dyoung@redhat.com>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: kexec@lists.infradead.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: x86-ml <x86@kernel.org>
Cc: Yi Wang <wang.yi59@zte.com.cn>
Link: https://lkml.kernel.org/r/20190423013007.17838-4-lijiang@redhat.com
---
arch/x86/kernel/crash.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 576b2e1bfc12..32c956705b8e 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -381,6 +381,12 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
walk_iomem_res_desc(IORES_DESC_ACPI_NV_STORAGE, flags, 0, -1, &cmd,
memmap_entry_callback);

+ /* Add e820 reserved ranges */
+ cmd.type = E820_TYPE_RESERVED;
+ flags = IORESOURCE_MEM;
+ walk_iomem_res_desc(IORES_DESC_RESERVED, flags, 0, -1, &cmd,
+ memmap_entry_callback);
+
/* Add crashk_low_res region */
if (crashk_low_res.end) {
ei.addr = crashk_low_res.start;
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