linux-kernel - [PATCH] iscsi_ibft: Fix finding the iBFT under Xen Dom 0

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Date:   Wed, 24 May 2023 17:05:58 +0100
From:   Ross Lagerwall <ross.lagerwall@...rix.com>
To:     <linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Peter Jones <pjones@...hat.com>,
        "Konrad Rzeszutek Wilk" <konrad@...nel.org>,
        Ross Lagerwall <ross.lagerwall@...rix.com>
Subject: [PATCH] iscsi_ibft: Fix finding the iBFT under Xen Dom 0

Since firmware doesn't indicate the iBFT in the E820, add a reserved
region so that it gets identity mapped when running as Dom 0 so that it
is possible to search for it. Move the call to reserve_ibft_region()
later so that it is called after the Xen identity mapping adjustments
are applied.

Finally, instead of using isa_bus_to_virt() which doesn't do the right
thing under Xen, use early_memremap() like the dmi_scan code does.

Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
---

It tested this to work under Xen and native Linux.

 arch/x86/kernel/setup.c            |  2 +-
 arch/x86/xen/setup.c               |  8 +++++++-
 drivers/firmware/iscsi_ibft_find.c | 24 +++++++++++++++++-------
 3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 16babff771bd..616b80507abd 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -796,7 +796,6 @@ static void __init early_reserve_memory(void)
 
 	memblock_x86_reserve_range_setup_data();
 
-	reserve_ibft_region();
 	reserve_bios_regions();
 	trim_snb_memory();
 }
@@ -1032,6 +1031,7 @@ void __init setup_arch(char **cmdline_p)
 	if (efi_enabled(EFI_BOOT))
 		efi_init();
 
+	reserve_ibft_region();
 	dmi_setup();
 
 	/*
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index c2be3efb2ba0..daab59df3b99 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -772,8 +772,14 @@ char * __init xen_memory_setup(void)
 	 * UNUSABLE regions in domUs are not handled and will need
 	 * a patch in the future.
 	 */
-	if (xen_initial_domain())
+	if (xen_initial_domain()) {
 		xen_ignore_unusable();
+		/* Reserve 0.5 MiB to 1 MiB region so iBFT can be found */
+		xen_e820_table.entries[xen_e820_table.nr_entries].addr = 0x80000;
+		xen_e820_table.entries[xen_e820_table.nr_entries].size = 0x80000;
+		xen_e820_table.entries[xen_e820_table.nr_entries].type = E820_TYPE_RESERVED;
+		xen_e820_table.nr_entries++;
+	}
 
 	/* Make sure the Xen-supplied memory map is well-ordered. */
 	e820__update_table(&xen_e820_table);
diff --git a/drivers/firmware/iscsi_ibft_find.c b/drivers/firmware/iscsi_ibft_find.c
index 94b49ccd23ac..e3c1449987dd 100644
--- a/drivers/firmware/iscsi_ibft_find.c
+++ b/drivers/firmware/iscsi_ibft_find.c
@@ -52,9 +52,9 @@ static const struct {
  */
 void __init reserve_ibft_region(void)
 {
-	unsigned long pos;
+	unsigned long pos, virt_pos = 0;
 	unsigned int len = 0;
-	void *virt;
+	void *virt = NULL;
 	int i;
 
 	ibft_phys_addr = 0;
@@ -70,13 +70,20 @@ void __init reserve_ibft_region(void)
 		 * so skip that area */
 		if (pos == VGA_MEM)
 			pos += VGA_SIZE;
-		virt = isa_bus_to_virt(pos);
+
+		/* Map page by page */
+		if (offset_in_page(pos) == 0) {
+			if (virt)
+				early_memunmap(virt, PAGE_SIZE);
+			virt = early_memremap_ro(pos, PAGE_SIZE);
+			virt_pos = pos;
+		}
 
 		for (i = 0; i < ARRAY_SIZE(ibft_signs); i++) {
-			if (memcmp(virt, ibft_signs[i].sign, IBFT_SIGN_LEN) ==
-			    0) {
+			if (memcmp(virt + (pos - virt_pos), ibft_signs[i].sign,
+				   IBFT_SIGN_LEN) == 0) {
 				unsigned long *addr =
-				    (unsigned long *)isa_bus_to_virt(pos + 4);
+				    (unsigned long *)(virt + pos - virt_pos + 4);
 				len = *addr;
 				/* if the length of the table extends past 1M,
 				 * the table cannot be valid. */
@@ -84,9 +91,12 @@ void __init reserve_ibft_region(void)
 					ibft_phys_addr = pos;
 					memblock_reserve(ibft_phys_addr, PAGE_ALIGN(len));
 					pr_info("iBFT found at %pa.\n", &ibft_phys_addr);
-					return;
+					goto out;
 				}
 			}
 		}
 	}
+
+out:
+	early_memunmap(virt, PAGE_SIZE);
 }
-- 
2.31.1