x86/EISA: Use memremap() to probe for the EISA BIOS signature

The area at the 0x0FFFD9 physical location in the PC memory space is
regular memory, traditionally ROM BIOS and more recently a copy of BIOS
code and data in RAM, write-protected.

Therefore use memremap() to get access to it rather than ioremap(),
avoiding issues in virtualization scenarios and complementing changes such
as commit f7750a7 ("x86, mpparse, x86/acpi, x86/PCI, x86/dmi, SFI: Use
memremap() for RAM mappings") or commit 5997efb ("x86/boot: Use
memremap() to map the MPF and MPC data").

Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/alpine.DEB.2.21.2408242025210.30766@angie.orcam.me.uk
Closes: https://lore.kernel.org/r/20240822095122.736522-1-kirill.shutemov@linux.intel.com

Author: maciej-w-rozycki

arch/x86/kernel/eisa.c

@@ -11,15 +11,15 @@
 
 static __init int eisa_bus_probe(void)
 {
-	void __iomem *p;
+	void *p;
 
 	if ((xen_pv_domain() && !xen_initial_domain()) || cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
 		return 0;
 
-	p = ioremap(0x0FFFD9, 4);
+	p = memremap(0x0FFFD9, 4, MEMREMAP_WB);
 	if (p && readl(p) == 'E' + ('I' << 8) + ('S' << 16) + ('A' << 24))
 		EISA_bus = 1;
-	iounmap(p);
+	memunmap(p);
 	return 0;
 }
 subsys_initcall(eisa_bus_probe);