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 ]
[ Srivatsa: Removed __ro_after_init for 4.4.y ]
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 Signed-off-by: Srivatsa S. Bhat srivatsa@csail.mit.edu Reviewed-by: Matt Helsley (VMware) matt.helsley@gmail.com Reviewed-by: Alexey Makhalov amakhalov@vmware.com Reviewed-by: Bo Gan ganb@vmware.com ---
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(-)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index 9510f5f..b7cdd1c 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -204,6 +204,7 @@ #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 */ diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index c786d01..ac2fdc96 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -199,6 +199,10 @@ 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[];
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 9b29414..4452f38 100644 --- 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> @@ -519,6 +520,26 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
if (cpu_has(c, X86_FEATURE_MWAITX)) use_mwaitx_delay(); + + 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) @@ -794,6 +815,11 @@ static void init_amd(struct cpuinfo_x86 *c) /* 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 diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index c37e211..b8911af 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -40,6 +40,13 @@ static u64 x86_spec_ctrl_base; */ static u64 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 x86_amd_ls_cfg_base; +u64 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 guest_spec_ctrl) } 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 __ssb_select_mitigation(void)
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 __ssb_select_mitigation(void) 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 diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 2f1d403..7405c86 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -851,6 +851,10 @@ static const __initconst struct x86_cpu_id cpu_no_spec_store_bypass[] = { { 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, }, {} };