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Subject[PATCH 4.9 46/87] x86/bugs/AMD: Add support to disable RDS on Fam[15,16,17]h if requested
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Woodhouse <dwmw@amazon.co.uk>

commit 764f3c21588a059cd783c6ba0734d4db2d72822d upstream

AMD does not need the Speculative Store Bypass mitigation to be enabled.

The parameters for this are already available and can be done via MSR
C001_1020. Each family uses a different bit in that MSR for this.

[ tglx: Expose the bit mask via a variable and move the actual MSR fiddling
into the bugs code as that's the right thing to do and also required
to prepare for dynamic enable/disable ]

Suggested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/nospec-branch.h | 4 ++++
arch/x86/kernel/cpu/amd.c | 26 ++++++++++++++++++++++++++
arch/x86/kernel/cpu/bugs.c | 27 ++++++++++++++++++++++++++-
arch/x86/kernel/cpu/common.c | 4 ++++
5 files changed, 61 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -205,6 +205,7 @@
#define X86_FEATURE_USE_IBPB ( 7*32+21) /* "" Indirect Branch Prediction Barrier enabled */
#define X86_FEATURE_USE_IBRS_FW ( 7*32+22) /* "" Use IBRS during runtime firmware calls */
#define X86_FEATURE_SPEC_STORE_BYPASS_DISABLE ( 7*32+23) /* "" Disable Speculative Store Bypass. */
+#define X86_FEATURE_AMD_RDS (7*32+24) /* "" AMD RDS implementation */

/* Virtualization flags: Linux defined, word 8 */
#define X86_FEATURE_TPR_SHADOW ( 8*32+ 0) /* Intel TPR Shadow */
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -244,6 +244,10 @@ enum ssb_mitigation {
SPEC_STORE_BYPASS_DISABLE,
};

+/* AMD specific Speculative Store Bypass MSR data */
+extern u64 x86_amd_ls_cfg_base;
+extern u64 x86_amd_ls_cfg_rds_mask;
+
extern char __indirect_thunk_start[];
extern char __indirect_thunk_end[];

--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -9,6 +9,7 @@
#include <asm/processor.h>
#include <asm/apic.h>
#include <asm/cpu.h>
+#include <asm/nospec-branch.h>
#include <asm/smp.h>
#include <asm/pci-direct.h>
#include <asm/delay.h>
@@ -542,6 +543,26 @@ static void bsp_init_amd(struct cpuinfo_
rdmsrl(MSR_FAM10H_NODE_ID, value);
nodes_per_socket = ((value >> 3) & 7) + 1;
}
+
+ if (c->x86 >= 0x15 && c->x86 <= 0x17) {
+ unsigned int bit;
+
+ switch (c->x86) {
+ case 0x15: bit = 54; break;
+ case 0x16: bit = 33; break;
+ case 0x17: bit = 10; break;
+ default: return;
+ }
+ /*
+ * Try to cache the base value so further operations can
+ * avoid RMW. If that faults, do not enable RDS.
+ */
+ if (!rdmsrl_safe(MSR_AMD64_LS_CFG, &x86_amd_ls_cfg_base)) {
+ setup_force_cpu_cap(X86_FEATURE_RDS);
+ setup_force_cpu_cap(X86_FEATURE_AMD_RDS);
+ x86_amd_ls_cfg_rds_mask = 1ULL << bit;
+ }
+ }
}

static void early_init_amd(struct cpuinfo_x86 *c)
@@ -827,6 +848,11 @@ static void init_amd(struct cpuinfo_x86
/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
if (!cpu_has(c, X86_FEATURE_XENPV))
set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+
+ if (boot_cpu_has(X86_FEATURE_AMD_RDS)) {
+ set_cpu_cap(c, X86_FEATURE_RDS);
+ set_cpu_cap(c, X86_FEATURE_AMD_RDS);
+ }
}

#ifdef CONFIG_X86_32
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -40,6 +40,13 @@ static u64 __ro_after_init x86_spec_ctrl
*/
static u64 __ro_after_init x86_spec_ctrl_mask = ~SPEC_CTRL_IBRS;

+/*
+ * AMD specific MSR info for Speculative Store Bypass control.
+ * x86_amd_ls_cfg_rds_mask is initialized in identify_boot_cpu().
+ */
+u64 __ro_after_init x86_amd_ls_cfg_base;
+u64 __ro_after_init x86_amd_ls_cfg_rds_mask;
+
void __init check_bugs(void)
{
identify_boot_cpu();
@@ -51,7 +58,8 @@ void __init check_bugs(void)

/*
* Read the SPEC_CTRL MSR to account for reserved bits which may
- * have unknown values.
+ * have unknown values. AMD64_LS_CFG MSR is cached in the early AMD
+ * init code as it is not enumerated and depends on the family.
*/
if (boot_cpu_has(X86_FEATURE_IBRS))
rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
@@ -153,6 +161,14 @@ void x86_spec_ctrl_restore_host(u64 gues
}
EXPORT_SYMBOL_GPL(x86_spec_ctrl_restore_host);

+static void x86_amd_rds_enable(void)
+{
+ u64 msrval = x86_amd_ls_cfg_base | x86_amd_ls_cfg_rds_mask;
+
+ if (boot_cpu_has(X86_FEATURE_AMD_RDS))
+ wrmsrl(MSR_AMD64_LS_CFG, msrval);
+}
+
#ifdef RETPOLINE
static bool spectre_v2_bad_module;

@@ -442,6 +458,11 @@ static enum ssb_mitigation_cmd __init __

switch (cmd) {
case SPEC_STORE_BYPASS_CMD_AUTO:
+ /*
+ * AMD platforms by default don't need SSB mitigation.
+ */
+ if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
+ break;
case SPEC_STORE_BYPASS_CMD_ON:
mode = SPEC_STORE_BYPASS_DISABLE;
break;
@@ -468,6 +489,7 @@ static enum ssb_mitigation_cmd __init __
x86_spec_ctrl_set(SPEC_CTRL_RDS);
break;
case X86_VENDOR_AMD:
+ x86_amd_rds_enable();
break;
}
}
@@ -489,6 +511,9 @@ void x86_spec_ctrl_setup_ap(void)
{
if (boot_cpu_has(X86_FEATURE_IBRS))
x86_spec_ctrl_set(x86_spec_ctrl_base & ~x86_spec_ctrl_mask);
+
+ if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
+ x86_amd_rds_enable();
}

#ifdef CONFIG_SYSFS
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -895,6 +895,10 @@ static const __initconst struct x86_cpu_
{ X86_VENDOR_CENTAUR, 5, },
{ X86_VENDOR_INTEL, 5, },
{ X86_VENDOR_NSC, 5, },
+ { X86_VENDOR_AMD, 0x12, },
+ { X86_VENDOR_AMD, 0x11, },
+ { X86_VENDOR_AMD, 0x10, },
+ { X86_VENDOR_AMD, 0xf, },
{ X86_VENDOR_ANY, 4, },
{}
};

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