[RFC][PATCH 24/34] x86/cpu: Establish 'min_cache_bits' configuration

Dave Hansen
2024-02-22T18:39:59Z

Continue moving towards a setup where code never tweaks 'boot_cpu_data'.

Code must establish their intent in 'x86_addr_config' and then later
code will use that config information to establish the system-wide
config.

The L1TF wants to tweak x86_cache_bits. Let it do this, but move
the code away from bugs.c so that ti can be easily called earlier
en boot.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

b/arch/x86/include/asm/processor.h | 6 +++++
b/arch/x86/kernel/cpu/bugs.c | 41 -------------------------------------
b/arch/x86/kernel/cpu/common.c | 2 +
b/arch/x86/kernel/cpu/intel.c | 40 ++++++++++++++++++++++++++++++++++++
4 files changed, 48 insertions(+), 41 deletions(-)

diff -puN arch/x86/include/asm/processor.h~bsp-min_cache_bits arch/x86/include/asm/processor.h
--- a/arch/x86/include/asm/processor.h~bsp-min_cache_bits 2024-02-22 10:09:00.220915031 -0800
+++ b/arch/x86/include/asm/processor.h 2024-02-22 10:09:00.224915188 -0800
@@ -177,6 +177,12 @@ struct x86_addr_config {
* will take place at a more coarse granularity.
*/
u8 cache_align_mult;
+
+ /*
+ * Specify a floor for the number of bits that the CPU
+ * caches comprehend. Used only for L1TF mitigation.
+ */
+ u8 min_cache_bits;
};

/*
diff -puN arch/x86/kernel/cpu/bugs.c~bsp-min_cache_bits arch/x86/kernel/cpu/bugs.c
--- a/arch/x86/kernel/cpu/bugs.c~bsp-min_cache_bits 2024-02-22 10:09:00.220915031 -0800
+++ b/arch/x86/kernel/cpu/bugs.c 2024-02-22 10:09:00.224915188 -0800
@@ -2237,45 +2237,6 @@ EXPORT_SYMBOL_GPL(l1tf_mitigation);
enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);

-/*
- * These CPUs all support 44bits physical address space internally in the
- * cache but CPUID can report a smaller number of physical address bits.
- *
- * The L1TF mitigation uses the top most address bit for the inversion of
- * non present PTEs. When the installed memory reaches into the top most
- * address bit due to memory holes, which has been observed on machines
- * which report 36bits physical address bits and have 32G RAM installed,
- * then the mitigation range check in l1tf_select_mitigation() triggers.
- * This is a false positive because the mitigation is still possible due to
- * the fact that the cache uses 44bit internally. Use the cache bits
- * instead of the reported physical bits and adjust them on the affected
- * machines to 44bit if the reported bits are less than 44.
- */
-static void override_cache_bits(struct cpuinfo_x86 *c)
-{
- if (c->x86 != 6)
- return;
-
- switch (c->x86_model) {
- case INTEL_FAM6_NEHALEM:
- case INTEL_FAM6_WESTMERE:
- case INTEL_FAM6_SANDYBRIDGE:
- case INTEL_FAM6_IVYBRIDGE:
- case INTEL_FAM6_HASWELL:
- case INTEL_FAM6_HASWELL_L:
- case INTEL_FAM6_HASWELL_G:
- case INTEL_FAM6_BROADWELL:
- case INTEL_FAM6_BROADWELL_G:
- case INTEL_FAM6_SKYLAKE_L:
- case INTEL_FAM6_SKYLAKE:
- case INTEL_FAM6_KABYLAKE_L:
- case INTEL_FAM6_KABYLAKE:
- if (c->x86_cache_bits < 44)
- c->x86_cache_bits = 44;
- break;
- }
-}
-
static void __init l1tf_select_mitigation(void)
{
u64 half_pa;
@@ -2288,8 +2249,6 @@ static void __init l1tf_select_mitigatio
else if (cpu_mitigations_auto_nosmt())
l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;

- override_cache_bits(&boot_cpu_data);
-
switch (l1tf_mitigation) {
case L1TF_MITIGATION_OFF:
case L1TF_MITIGATION_FLUSH_NOWARN:
diff -puN arch/x86/kernel/cpu/common.c~bsp-min_cache_bits arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~bsp-min_cache_bits 2024-02-22 10:09:00.220915031 -0800
+++ b/arch/x86/kernel/cpu/common.c 2024-02-22 10:09:00.228915345 -0800
@@ -1139,6 +1139,8 @@ void get_cpu_address_sizes(struct cpuinf
x86_config.clflush_size = detect_clflush_size(c);

c->x86_cache_bits = x86_config.phys_bits;
+ if (c->x86_cache_bits < bsp_addr_config.min_cache_bits)
+ c->x86_cache_bits = bsp_addr_config.min_cache_bits;

x86_config.cache_alignment = x86_clflush_size();
if (bsp_addr_config.cache_align_mult)
diff -puN arch/x86/kernel/cpu/intel.c~bsp-min_cache_bits arch/x86/kernel/cpu/intel.c
--- a/arch/x86/kernel/cpu/intel.c~bsp-min_cache_bits 2024-02-22 10:09:00.224915188 -0800
+++ b/arch/x86/kernel/cpu/intel.c 2024-02-22 10:09:00.228915345 -0800
@@ -395,6 +395,44 @@ detect_keyid_bits:
return keyid_bits;
}

+/*
+ * These CPUs all support 44bits physical address space internally in the
+ * cache but CPUID can report a smaller number of physical address bits.
+ *
+ * The L1TF mitigation uses the top most address bit for the inversion of
+ * non present PTEs. When the installed memory reaches into the top most
+ * address bit due to memory holes, which has been observed on machines
+ * which report 36bits physical address bits and have 32G RAM installed,
+ * then the mitigation range check in l1tf_select_mitigation() triggers.
+ * This is a false positive because the mitigation is still possible due to
+ * the fact that the cache uses 44bit internally. Use the cache bits
+ * instead of the reported physical bits and adjust them on the affected
+ * machines to 44bit if the reported bits are less than 44.
+ */
+static void set_min_cache_bits(struct cpuinfo_x86 *c)
+{
+ if (c->x86 != 6)
+ return;
+
+ switch (c->x86_model) {
+ case INTEL_FAM6_NEHALEM:
+ case INTEL_FAM6_WESTMERE:
+ case INTEL_FAM6_SANDYBRIDGE:
+ case INTEL_FAM6_IVYBRIDGE:
+ case INTEL_FAM6_HASWELL:
+ case INTEL_FAM6_HASWELL_L:
+ case INTEL_FAM6_HASWELL_G:
+ case INTEL_FAM6_BROADWELL:
+ case INTEL_FAM6_BROADWELL_G:
+ case INTEL_FAM6_SKYLAKE_L:
+ case INTEL_FAM6_SKYLAKE:
+ case INTEL_FAM6_KABYLAKE_L:
+ case INTEL_FAM6_KABYLAKE:
+ bsp_addr_config.min_cache_bits = 44;
+ break;
+ }
+}
+
static void bsp_init_intel(struct cpuinfo_x86 *c)
{
int keyid_bits = 0;
@@ -418,6 +456,8 @@ static void bsp_init_intel(struct cpuinf
/* Netburst reports 64 bytes clflush size, but does IO in 128 bytes */
if (c->x86 == 15)
bsp_addr_config.cache_align_mult = 2;
+
+ set_min_cache_bits(c);
}

#ifdef CONFIG_X86_32
_