Re: [PATCH v4 02/12] x86/mtrr: optimize mtrr_calc_physbits()

[Borislav Petkov]

On Mon, Mar 06, 2023 at 05:34:15PM +0100, Juergen Gross wrote:
> Optimize mtrr_calc_physbits() for better readability.
> 
> Drop a stale comment, as reality has made it obsolete.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V3:
> - new patch, split off from previous patch (Boris Petkov)
> ---
>  arch/x86/kernel/cpu/mtrr/mtrr.c | 19 +++----------------
>  1 file changed, 3 insertions(+), 16 deletions(-)

Optimize some more:

---
From: Juergen Gross <jgross@xxxxxxxx>
Date: Mon, 6 Mar 2023 17:34:15 +0100
Subject: [PATCH] x86/mtrr: Optimize mtrr_calc_physbits()

Optimize mtrr_calc_physbits() for better readability.

Drop a stale comment, as reality has made it obsolete.

  [ bp:
   - s/mtrr/MTRR/
   - s/boot_cpu_has/cpu_feature_enabled/
   - use GENMASK_ULL
   - simplify. ]

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230306163425.8324-3-jgross@xxxxxxxx
---
 arch/x86/kernel/cpu/mtrr/mtrr.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
index 8310bdb111d0..deb22e989105 100644
--- a/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -619,8 +619,6 @@ static struct syscore_ops mtrr_syscore_ops = {
 
 int __initdata changed_by_mtrr_cleanup;
 
-#define SIZE_OR_MASK_BITS(n)  (~((1ULL << ((n) - PAGE_SHIFT)) - 1))
-
 static unsigned int __init mtrr_calc_physbits(bool generic)
 {
 	unsigned int phys_addr;
@@ -628,15 +626,8 @@ static unsigned int __init mtrr_calc_physbits(bool generic)
 	phys_addr = 32;
 
 	if (generic) {
-		size_or_mask = SIZE_OR_MASK_BITS(36);
-		size_and_mask = 0x00f00000;
 		phys_addr = 36;
 
-		/*
-		 * This is an AMD specific MSR, but we assume(hope?) that
-		 * Intel will implement it too when they extend the address
-		 * bus of the Xeon.
-		 */
 		if (cpuid_eax(0x80000000) >= 0x80000008) {
 			phys_addr = cpuid_eax(0x80000008) & 0xff;
 			/* CPUID workaround for Intel 0F33/0F34 CPU */
@@ -647,41 +638,37 @@ static unsigned int __init mtrr_calc_physbits(bool generic)
 			     boot_cpu_data.x86_stepping == 0x4))
 				phys_addr = 36;
 
-			size_or_mask = SIZE_OR_MASK_BITS(phys_addr);
-			size_and_mask = ~size_or_mask & 0xfffff00000ULL;
 		} else if (boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR &&
 			   boot_cpu_data.x86 == 6) {
 			/*
 			 * VIA C* family have Intel style MTRRs,
 			 * but don't support PAE
 			 */
-			size_or_mask = SIZE_OR_MASK_BITS(32);
-			size_and_mask = 0;
 			phys_addr = 32;
 		}
-	} else {
-		size_or_mask = SIZE_OR_MASK_BITS(32);
-		size_and_mask = 0;
 	}
 
+	size_or_mask  = ~GENMASK_ULL(phys_addr - PAGE_SHIFT, 0);
+	size_and_mask = ~size_or_mask & GENMASK_ULL(39, 20);
+
 	return phys_addr;
 }
 
 /**
- * mtrr_bp_init - initialize mtrrs on the boot CPU
+ * mtrr_bp_init - initialize MTRRs on the boot CPU
  *
  * This needs to be called early; before any of the other CPUs are
  * initialized (i.e. before smp_init()).
- *
  */
 void __init mtrr_bp_init(void)
 {
+	bool generic_mtrrs = cpu_feature_enabled(X86_FEATURE_MTRR);
 	const char *why = "(not available)";
 	unsigned int phys_addr;
 
-	phys_addr = mtrr_calc_physbits(boot_cpu_has(X86_FEATURE_MTRR));
+	phys_addr = mtrr_calc_physbits(generic_mtrrs);
 
-	if (boot_cpu_has(X86_FEATURE_MTRR)) {
+	if (generic_mtrrs) {
 		mtrr_if = &generic_mtrr_ops;
 	} else {
 		switch (boot_cpu_data.x86_vendor) {
-- 
2.35.1

-- 
Regards/Gruss,
    Boris.

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