x86/MTRR: optionally print boot time state

... helping diagnosing eventual issues. Taken from Linux, with quite
a bit of cleanup.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
To preempt questions: The command line option name was chosen following
the one that had been transiently in use in Linux. If the dot in it is
considered awkward, I'm not too fuzzed about this versus another
reasonably named option.

--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -676,6 +676,13 @@ Specify if the MMConfig space should be 
 
 Force Xen to (not) use PCI-MSI, even if ACPI FADT says otherwise.
 
+### mtrr.show
+> `= <boolean>`
+
+> Default: `false`
+
+Print boot time MTRR state (x86 only).
+
 ### mwait-idle
 > `= <boolean>`
 
--- a/xen/arch/x86/cpu/mtrr/generic.c
+++ b/xen/arch/x86/cpu/mtrr/generic.c
@@ -84,11 +84,113 @@ void __init get_mtrr_state(void)
 	rdmsrl(MSR_MTRRcap, mtrr_state.mtrr_cap);
 }
 
+static bool_t __initdata mtrr_show;
+boolean_param("mtrr.show", mtrr_show);
+
+static const char *__init mtrr_attrib_to_str(mtrr_type x)
+{
+	static const char __initconst strings[MTRR_NUM_TYPES][16] =
+	{
+		[0 ... MTRR_NUM_TYPES - 1] = "?",
+		[MTRR_TYPE_UNCACHABLE]     = "uncachable",
+		[MTRR_TYPE_WRCOMB]         = "write-combining",
+		[MTRR_TYPE_WRTHROUGH]      = "write-through",
+		[MTRR_TYPE_WRPROT]         = "write-protect",
+		[MTRR_TYPE_WRBACK]         = "write-back",
+	};
+
+	return x < MTRR_NUM_TYPES ? strings[x] : "?";
+}
+
+static unsigned int __initdata last_fixed_start;
+static unsigned int __initdata last_fixed_end;
+static mtrr_type __initdata last_fixed_type;
+
+static void __init print_fixed_last(const char *level)
+{
+	if (!last_fixed_end)
+		return;
+
+	printk("%s  %05x-%05x %s\n", level, last_fixed_start,
+	       last_fixed_end - 1, mtrr_attrib_to_str(last_fixed_type));
+
+	last_fixed_end = 0;
+}
+
+static void __init update_fixed_last(unsigned int base, unsigned int end,
+				     mtrr_type type)
+{
+	last_fixed_start = base;
+	last_fixed_end = end;
+	last_fixed_type = type;
+}
+
+static void __init print_fixed(unsigned int base, unsigned int step,
+			       const mtrr_type *types, const char *level)
+{
+	unsigned i;
+
+	for (i = 0; i < 8; ++i, ++types, base += step) {
+		if (last_fixed_end == 0) {
+			update_fixed_last(base, base + step, *types);
+			continue;
+		}
+		if (last_fixed_end == base && last_fixed_type == *types) {
+			last_fixed_end = base + step;
+			continue;
+		}
+		/* new segments: gap or different type */
+		print_fixed_last(level);
+		update_fixed_last(base, base + step, *types);
+	}
+}
+
+static void __init print_mtrr_state(const char *level)
+{
+	unsigned int i;
+	int width;
+
+	printk("%sMTRR default type: %s\n", level,
+	       mtrr_attrib_to_str(mtrr_state.def_type));
+	if (mtrr_state.have_fixed) {
+		const mtrr_type *fr = mtrr_state.fixed_ranges;
+		const struct fixed_range_block *block = fixed_range_blocks;
+		unsigned int base = 0, step = 0x10000;
+
+		printk("%sMTRR fixed ranges %sabled:\n", level,
+		       mtrr_state.enabled & 1 ? "en" : "dis");
+		for (; block->ranges; ++block, step >>= 2) {
+			for (i = 0; i < block->ranges; ++i, fr += 8) {
+				print_fixed(base, step, fr, level);
+				base += 8 * step;
+			}
+		}
+		print_fixed_last(level);
+	}
+	printk("%sMTRR variable ranges %sabled:\n", level,
+	       mtrr_state.enabled & 2 ? "en" : "dis");
+	width = (paddr_bits - PAGE_SHIFT + 3) / 4;
+
+	for (i = 0; i < num_var_ranges; ++i) {
+		if (mtrr_state.var_ranges[i].mask & MTRR_PHYSMASK_VALID)
+			printk("%s  %u base %0*"PRIx64"000 mask %0*"PRIx64"000 %s\n",
+			       level, i,
+			       width, mtrr_state.var_ranges[i].base >> 12,
+			       width, mtrr_state.var_ranges[i].mask >> 12,
+			       mtrr_attrib_to_str(mtrr_state.var_ranges[i].base &
+			                          MTRR_PHYSBASE_TYPE_MASK));
+		else
+			printk("%s  %u disabled\n", level, i);
+	}
+}
+
 /*  Some BIOS's are fucked and don't set all MTRRs the same!  */
 void __init mtrr_state_warn(void)
 {
 	unsigned long mask = smp_changes_mask;
 
+	if (mtrr_show)
+		print_mtrr_state(mask ? KERN_WARNING : "");
 	if (!mask)
 		return;
 	if (mask & MTRR_CHANGE_MASK_FIXED)
@@ -99,6 +201,8 @@ void __init mtrr_state_warn(void)
 		printk(KERN_WARNING "mtrr: your CPUs had inconsistent MTRRdefType settings\n");
 	printk(KERN_INFO "mtrr: probably your BIOS does not setup all CPUs.\n");
 	printk(KERN_INFO "mtrr: corrected configuration.\n");
+	if (!mtrr_show)
+		print_mtrr_state(KERN_INFO);
 }
 
 /* Doesn't attempt to pass an error out to MTRR users