linux-kernel - Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on kexec-ed kernel

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Date:   Fri, 12 Apr 2019 10:49:56 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Junichi Nomura <j-nomura@...jp.nec.com>
Cc:     Dave Young <dyoung@...hat.com>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Baoquan He <bhe@...hat.com>, Kairui Song <kasong@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on
 kexec-ed kernel

On Fri, Apr 12, 2019 at 02:54:17AM +0000, Junichi Nomura wrote:
> Without #ifdef CONFIG_X86_64, I got compiler warnings on 32bit build
> about casting u64 to pointer.

Yah, stupid ifdeffery.

> We need #ifdef CONFIG_EFI to avoid build failure about undefined
> __efi_get_rsdp_addr().

diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
index c3020e2d8f67..4b1d4a0a4269 100644
--- a/arch/x86/boot/compressed/acpi.c
+++ b/arch/x86/boot/compressed/acpi.c
@@ -46,7 +46,6 @@ static acpi_physical_address get_acpi_rsdp(void)
 	return addr;
 }
 
-#ifdef CONFIG_EFI
 /*
  * Search EFI system tables for RSDP.  If both ACPI_20_TABLE_GUID and
  * ACPI_TABLE_GUID are found, take the former, which has more features.
@@ -56,6 +55,8 @@ __efi_get_rsdp_addr(unsigned long config_tables, unsigned int nr_tables,
 		    bool efi_64)
 {
 	acpi_physical_address rsdp_addr = 0;
+
+#ifdef CONFIG_EFI
 	int i;
 
 	/* Get EFI tables from systab. */
@@ -85,10 +86,9 @@ __efi_get_rsdp_addr(unsigned long config_tables, unsigned int nr_tables,
 		else if (!(efi_guidcmp(guid, ACPI_20_TABLE_GUID)))
 			return table;
 	}
-
+#endif
 	return rsdp_addr;
 }
-#endif
 
 /* EFI/kexec support is 64-bit only. */
 #ifdef CONFIG_X86_64
---

> I think that should be the other way around:

No, it shouldn't.

kexec_get_rsdp_addr() must do:

	if (!kexec_kernel)
		return 0:

        esd = (struct efi_setup_data *)get_kexec_setup_data_addr();
        if (!esd)
                return EFI_SETUP_DATA_INVALID;

	...

Now I need to go figure out whether there's a reliable way to know in
the kexec kernel that it *is* a kexec kernel.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.