summaryrefslogtreecommitdiffstats
path: root/arch/x86
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-18 18:43:28 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-18 18:43:28 +0000
commitd8e7eb3d28f5c8e73b91bc95b2f01391711b1839 (patch)
tree4281b77072f7954692604850497ede427d7f9e22 /arch/x86
parentAdding debian version 6.7.7-1. (diff)
downloadlinux-d8e7eb3d28f5c8e73b91bc95b2f01391711b1839.tar.xz
linux-d8e7eb3d28f5c8e73b91bc95b2f01391711b1839.zip
Merging upstream version 6.7.9.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/entry/entry_32.S3
-rw-r--r--arch/x86/entry/entry_64.S11
-rw-r--r--arch/x86/entry/entry_64_compat.S1
-rw-r--r--arch/x86/include/asm/entry-common.h1
-rw-r--r--arch/x86/include/asm/nospec-branch.h12
-rw-r--r--arch/x86/kernel/cpu/bugs.c15
-rw-r--r--arch/x86/kernel/cpu/common.c4
-rw-r--r--arch/x86/kernel/cpu/intel.c178
-rw-r--r--arch/x86/kernel/e820.c8
-rw-r--r--arch/x86/kernel/nmi.c3
-rw-r--r--arch/x86/kvm/vmx/run_flags.h7
-rw-r--r--arch/x86/kvm/vmx/vmenter.S9
-rw-r--r--arch/x86/kvm/vmx/vmx.c20
13 files changed, 146 insertions, 126 deletions
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index c73047bf9f..fba4276468 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -885,6 +885,7 @@ SYM_FUNC_START(entry_SYSENTER_32)
BUG_IF_WRONG_CR3 no_user_check=1
popfl
popl %eax
+ CLEAR_CPU_BUFFERS
/*
* Return back to the vDSO, which will pop ecx and edx.
@@ -954,6 +955,7 @@ restore_all_switch_stack:
/* Restore user state */
RESTORE_REGS pop=4 # skip orig_eax/error_code
+ CLEAR_CPU_BUFFERS
.Lirq_return:
/*
* ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
@@ -1146,6 +1148,7 @@ SYM_CODE_START(asm_exc_nmi)
/* Not on SYSENTER stack. */
call exc_nmi
+ CLEAR_CPU_BUFFERS
jmp .Lnmi_return
.Lnmi_from_sysenter_stack:
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index de6469dffe..bdb17fad5d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -161,6 +161,7 @@ syscall_return_via_sysret:
SYM_INNER_LABEL(entry_SYSRETQ_unsafe_stack, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
swapgs
+ CLEAR_CPU_BUFFERS
sysretq
SYM_INNER_LABEL(entry_SYSRETQ_end, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
@@ -601,6 +602,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
/* Restore RDI. */
popq %rdi
swapgs
+ CLEAR_CPU_BUFFERS
jmp .Lnative_iret
@@ -712,6 +714,8 @@ native_irq_return_ldt:
*/
popq %rax /* Restore user RAX */
+ CLEAR_CPU_BUFFERS
+
/*
* RSP now points to an ordinary IRET frame, except that the page
* is read-only and RSP[31:16] are preloaded with the userspace
@@ -1439,6 +1443,12 @@ nmi_restore:
movq $0, 5*8(%rsp) /* clear "NMI executing" */
/*
+ * Skip CLEAR_CPU_BUFFERS here, since it only helps in rare cases like
+ * NMI in kernel after user state is restored. For an unprivileged user
+ * these conditions are hard to meet.
+ */
+
+ /*
* iretq reads the "iret" frame and exits the NMI stack in a
* single instruction. We are returning to kernel mode, so this
* cannot result in a fault. Similarly, we don't need to worry
@@ -1455,6 +1465,7 @@ SYM_CODE_START(entry_SYSCALL32_ignore)
UNWIND_HINT_END_OF_STACK
ENDBR
mov $-ENOSYS, %eax
+ CLEAR_CPU_BUFFERS
sysretl
SYM_CODE_END(entry_SYSCALL32_ignore)
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index de94e2e84e..eabf48c4d4 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -270,6 +270,7 @@ SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
xorl %r9d, %r9d
xorl %r10d, %r10d
swapgs
+ CLEAR_CPU_BUFFERS
sysretl
SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index ce8f50192a..7e523bb3d2 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -91,7 +91,6 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
static __always_inline void arch_exit_to_user_mode(void)
{
- mds_user_clear_cpu_buffers();
amd_clear_divider();
}
#define arch_exit_to_user_mode arch_exit_to_user_mode
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 2519615936..d15b35815e 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -540,7 +540,6 @@ DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp);
DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
-DECLARE_STATIC_KEY_FALSE(mds_user_clear);
DECLARE_STATIC_KEY_FALSE(mds_idle_clear);
DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
@@ -575,17 +574,6 @@ static __always_inline void mds_clear_cpu_buffers(void)
}
/**
- * mds_user_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability
- *
- * Clear CPU buffers if the corresponding static key is enabled
- */
-static __always_inline void mds_user_clear_cpu_buffers(void)
-{
- if (static_branch_likely(&mds_user_clear))
- mds_clear_cpu_buffers();
-}
-
-/**
* mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability
*
* Clear CPU buffers if the corresponding static key is enabled
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bb0ab8466b..48d049cd74 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -111,9 +111,6 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
/* Control unconditional IBPB in switch_mm() */
DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
-/* Control MDS CPU buffer clear before returning to user space */
-DEFINE_STATIC_KEY_FALSE(mds_user_clear);
-EXPORT_SYMBOL_GPL(mds_user_clear);
/* Control MDS CPU buffer clear before idling (halt, mwait) */
DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
EXPORT_SYMBOL_GPL(mds_idle_clear);
@@ -252,7 +249,7 @@ static void __init mds_select_mitigation(void)
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
- static_branch_enable(&mds_user_clear);
+ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
(mds_nosmt || cpu_mitigations_auto_nosmt()))
@@ -356,7 +353,7 @@ static void __init taa_select_mitigation(void)
* For guests that can't determine whether the correct microcode is
* present on host, enable the mitigation for UCODE_NEEDED as well.
*/
- static_branch_enable(&mds_user_clear);
+ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (taa_nosmt || cpu_mitigations_auto_nosmt())
cpu_smt_disable(false);
@@ -424,7 +421,7 @@ static void __init mmio_select_mitigation(void)
*/
if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
boot_cpu_has(X86_FEATURE_RTM)))
- static_branch_enable(&mds_user_clear);
+ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
else
static_branch_enable(&mmio_stale_data_clear);
@@ -484,12 +481,12 @@ static void __init md_clear_update_mitigation(void)
if (cpu_mitigations_off())
return;
- if (!static_key_enabled(&mds_user_clear))
+ if (!boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
goto out;
/*
- * mds_user_clear is now enabled. Update MDS, TAA and MMIO Stale Data
- * mitigation, if necessary.
+ * X86_FEATURE_CLEAR_CPU_BUF is now enabled. Update MDS, TAA and MMIO
+ * Stale Data mitigation, if necessary.
*/
if (mds_mitigation == MDS_MITIGATION_OFF &&
boot_cpu_has_bug(X86_BUG_MDS)) {
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 98f7ea6b93..34cac9ea19 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1596,6 +1596,7 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
get_cpu_vendor(c);
get_cpu_cap(c);
setup_force_cpu_cap(X86_FEATURE_CPUID);
+ get_cpu_address_sizes(c);
cpu_parse_early_param();
if (this_cpu->c_early_init)
@@ -1608,10 +1609,9 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
this_cpu->c_bsp_init(c);
} else {
setup_clear_cpu_cap(X86_FEATURE_CPUID);
+ get_cpu_address_sizes(c);
}
- get_cpu_address_sizes(c);
-
setup_force_cpu_cap(X86_FEATURE_ALWAYS);
cpu_set_bug_bits(c);
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index a927a8fc96..40dec9b56f 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -184,6 +184,90 @@ static bool bad_spectre_microcode(struct cpuinfo_x86 *c)
return false;
}
+#define MSR_IA32_TME_ACTIVATE 0x982
+
+/* Helpers to access TME_ACTIVATE MSR */
+#define TME_ACTIVATE_LOCKED(x) (x & 0x1)
+#define TME_ACTIVATE_ENABLED(x) (x & 0x2)
+
+#define TME_ACTIVATE_POLICY(x) ((x >> 4) & 0xf) /* Bits 7:4 */
+#define TME_ACTIVATE_POLICY_AES_XTS_128 0
+
+#define TME_ACTIVATE_KEYID_BITS(x) ((x >> 32) & 0xf) /* Bits 35:32 */
+
+#define TME_ACTIVATE_CRYPTO_ALGS(x) ((x >> 48) & 0xffff) /* Bits 63:48 */
+#define TME_ACTIVATE_CRYPTO_AES_XTS_128 1
+
+/* Values for mktme_status (SW only construct) */
+#define MKTME_ENABLED 0
+#define MKTME_DISABLED 1
+#define MKTME_UNINITIALIZED 2
+static int mktme_status = MKTME_UNINITIALIZED;
+
+static void detect_tme_early(struct cpuinfo_x86 *c)
+{
+ u64 tme_activate, tme_policy, tme_crypto_algs;
+ int keyid_bits = 0, nr_keyids = 0;
+ static u64 tme_activate_cpu0 = 0;
+
+ rdmsrl(MSR_IA32_TME_ACTIVATE, tme_activate);
+
+ if (mktme_status != MKTME_UNINITIALIZED) {
+ if (tme_activate != tme_activate_cpu0) {
+ /* Broken BIOS? */
+ pr_err_once("x86/tme: configuration is inconsistent between CPUs\n");
+ pr_err_once("x86/tme: MKTME is not usable\n");
+ mktme_status = MKTME_DISABLED;
+
+ /* Proceed. We may need to exclude bits from x86_phys_bits. */
+ }
+ } else {
+ tme_activate_cpu0 = tme_activate;
+ }
+
+ if (!TME_ACTIVATE_LOCKED(tme_activate) || !TME_ACTIVATE_ENABLED(tme_activate)) {
+ pr_info_once("x86/tme: not enabled by BIOS\n");
+ mktme_status = MKTME_DISABLED;
+ return;
+ }
+
+ if (mktme_status != MKTME_UNINITIALIZED)
+ goto detect_keyid_bits;
+
+ pr_info("x86/tme: enabled by BIOS\n");
+
+ tme_policy = TME_ACTIVATE_POLICY(tme_activate);
+ if (tme_policy != TME_ACTIVATE_POLICY_AES_XTS_128)
+ pr_warn("x86/tme: Unknown policy is active: %#llx\n", tme_policy);
+
+ tme_crypto_algs = TME_ACTIVATE_CRYPTO_ALGS(tme_activate);
+ if (!(tme_crypto_algs & TME_ACTIVATE_CRYPTO_AES_XTS_128)) {
+ pr_err("x86/mktme: No known encryption algorithm is supported: %#llx\n",
+ tme_crypto_algs);
+ mktme_status = MKTME_DISABLED;
+ }
+detect_keyid_bits:
+ keyid_bits = TME_ACTIVATE_KEYID_BITS(tme_activate);
+ nr_keyids = (1UL << keyid_bits) - 1;
+ if (nr_keyids) {
+ pr_info_once("x86/mktme: enabled by BIOS\n");
+ pr_info_once("x86/mktme: %d KeyIDs available\n", nr_keyids);
+ } else {
+ pr_info_once("x86/mktme: disabled by BIOS\n");
+ }
+
+ if (mktme_status == MKTME_UNINITIALIZED) {
+ /* MKTME is usable */
+ mktme_status = MKTME_ENABLED;
+ }
+
+ /*
+ * KeyID bits effectively lower the number of physical address
+ * bits. Update cpuinfo_x86::x86_phys_bits accordingly.
+ */
+ c->x86_phys_bits -= keyid_bits;
+}
+
static void early_init_intel(struct cpuinfo_x86 *c)
{
u64 misc_enable;
@@ -322,6 +406,13 @@ static void early_init_intel(struct cpuinfo_x86 *c)
*/
if (detect_extended_topology_early(c) < 0)
detect_ht_early(c);
+
+ /*
+ * Adjust the number of physical bits early because it affects the
+ * valid bits of the MTRR mask registers.
+ */
+ if (cpu_has(c, X86_FEATURE_TME))
+ detect_tme_early(c);
}
static void bsp_init_intel(struct cpuinfo_x86 *c)
@@ -482,90 +573,6 @@ static void srat_detect_node(struct cpuinfo_x86 *c)
#endif
}
-#define MSR_IA32_TME_ACTIVATE 0x982
-
-/* Helpers to access TME_ACTIVATE MSR */
-#define TME_ACTIVATE_LOCKED(x) (x & 0x1)
-#define TME_ACTIVATE_ENABLED(x) (x & 0x2)
-
-#define TME_ACTIVATE_POLICY(x) ((x >> 4) & 0xf) /* Bits 7:4 */
-#define TME_ACTIVATE_POLICY_AES_XTS_128 0
-
-#define TME_ACTIVATE_KEYID_BITS(x) ((x >> 32) & 0xf) /* Bits 35:32 */
-
-#define TME_ACTIVATE_CRYPTO_ALGS(x) ((x >> 48) & 0xffff) /* Bits 63:48 */
-#define TME_ACTIVATE_CRYPTO_AES_XTS_128 1
-
-/* Values for mktme_status (SW only construct) */
-#define MKTME_ENABLED 0
-#define MKTME_DISABLED 1
-#define MKTME_UNINITIALIZED 2
-static int mktme_status = MKTME_UNINITIALIZED;
-
-static void detect_tme(struct cpuinfo_x86 *c)
-{
- u64 tme_activate, tme_policy, tme_crypto_algs;
- int keyid_bits = 0, nr_keyids = 0;
- static u64 tme_activate_cpu0 = 0;
-
- rdmsrl(MSR_IA32_TME_ACTIVATE, tme_activate);
-
- if (mktme_status != MKTME_UNINITIALIZED) {
- if (tme_activate != tme_activate_cpu0) {
- /* Broken BIOS? */
- pr_err_once("x86/tme: configuration is inconsistent between CPUs\n");
- pr_err_once("x86/tme: MKTME is not usable\n");
- mktme_status = MKTME_DISABLED;
-
- /* Proceed. We may need to exclude bits from x86_phys_bits. */
- }
- } else {
- tme_activate_cpu0 = tme_activate;
- }
-
- if (!TME_ACTIVATE_LOCKED(tme_activate) || !TME_ACTIVATE_ENABLED(tme_activate)) {
- pr_info_once("x86/tme: not enabled by BIOS\n");
- mktme_status = MKTME_DISABLED;
- return;
- }
-
- if (mktme_status != MKTME_UNINITIALIZED)
- goto detect_keyid_bits;
-
- pr_info("x86/tme: enabled by BIOS\n");
-
- tme_policy = TME_ACTIVATE_POLICY(tme_activate);
- if (tme_policy != TME_ACTIVATE_POLICY_AES_XTS_128)
- pr_warn("x86/tme: Unknown policy is active: %#llx\n", tme_policy);
-
- tme_crypto_algs = TME_ACTIVATE_CRYPTO_ALGS(tme_activate);
- if (!(tme_crypto_algs & TME_ACTIVATE_CRYPTO_AES_XTS_128)) {
- pr_err("x86/mktme: No known encryption algorithm is supported: %#llx\n",
- tme_crypto_algs);
- mktme_status = MKTME_DISABLED;
- }
-detect_keyid_bits:
- keyid_bits = TME_ACTIVATE_KEYID_BITS(tme_activate);
- nr_keyids = (1UL << keyid_bits) - 1;
- if (nr_keyids) {
- pr_info_once("x86/mktme: enabled by BIOS\n");
- pr_info_once("x86/mktme: %d KeyIDs available\n", nr_keyids);
- } else {
- pr_info_once("x86/mktme: disabled by BIOS\n");
- }
-
- if (mktme_status == MKTME_UNINITIALIZED) {
- /* MKTME is usable */
- mktme_status = MKTME_ENABLED;
- }
-
- /*
- * KeyID bits effectively lower the number of physical address
- * bits. Update cpuinfo_x86::x86_phys_bits accordingly.
- */
- c->x86_phys_bits -= keyid_bits;
-}
-
static void init_cpuid_fault(struct cpuinfo_x86 *c)
{
u64 msr;
@@ -702,9 +709,6 @@ static void init_intel(struct cpuinfo_x86 *c)
init_ia32_feat_ctl(c);
- if (cpu_has(c, X86_FEATURE_TME))
- detect_tme(c);
-
init_intel_misc_features(c);
split_lock_init();
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index fb8cf95338..b66f540de0 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1017,10 +1017,12 @@ void __init e820__reserve_setup_data(void)
e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
/*
- * SETUP_EFI and SETUP_IMA are supplied by kexec and do not need
- * to be reserved.
+ * SETUP_EFI, SETUP_IMA and SETUP_RNG_SEED are supplied by
+ * kexec and do not need to be reserved.
*/
- if (data->type != SETUP_EFI && data->type != SETUP_IMA)
+ if (data->type != SETUP_EFI &&
+ data->type != SETUP_IMA &&
+ data->type != SETUP_RNG_SEED)
e820__range_update_kexec(pa_data,
sizeof(*data) + data->len,
E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 17e955ab69..3082cf24b6 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -563,9 +563,6 @@ nmi_restart:
}
if (this_cpu_dec_return(nmi_state))
goto nmi_restart;
-
- if (user_mode(regs))
- mds_user_clear_cpu_buffers();
}
#if IS_ENABLED(CONFIG_KVM_INTEL)
diff --git a/arch/x86/kvm/vmx/run_flags.h b/arch/x86/kvm/vmx/run_flags.h
index edc3f16cc1..6a9bfdfbb6 100644
--- a/arch/x86/kvm/vmx/run_flags.h
+++ b/arch/x86/kvm/vmx/run_flags.h
@@ -2,7 +2,10 @@
#ifndef __KVM_X86_VMX_RUN_FLAGS_H
#define __KVM_X86_VMX_RUN_FLAGS_H
-#define VMX_RUN_VMRESUME (1 << 0)
-#define VMX_RUN_SAVE_SPEC_CTRL (1 << 1)
+#define VMX_RUN_VMRESUME_SHIFT 0
+#define VMX_RUN_SAVE_SPEC_CTRL_SHIFT 1
+
+#define VMX_RUN_VMRESUME BIT(VMX_RUN_VMRESUME_SHIFT)
+#define VMX_RUN_SAVE_SPEC_CTRL BIT(VMX_RUN_SAVE_SPEC_CTRL_SHIFT)
#endif /* __KVM_X86_VMX_RUN_FLAGS_H */
diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S
index be275a0410..139960deb7 100644
--- a/arch/x86/kvm/vmx/vmenter.S
+++ b/arch/x86/kvm/vmx/vmenter.S
@@ -139,7 +139,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
mov (%_ASM_SP), %_ASM_AX
/* Check if vmlaunch or vmresume is needed */
- test $VMX_RUN_VMRESUME, %ebx
+ bt $VMX_RUN_VMRESUME_SHIFT, %ebx
/* Load guest registers. Don't clobber flags. */
mov VCPU_RCX(%_ASM_AX), %_ASM_CX
@@ -161,8 +161,11 @@ SYM_FUNC_START(__vmx_vcpu_run)
/* Load guest RAX. This kills the @regs pointer! */
mov VCPU_RAX(%_ASM_AX), %_ASM_AX
- /* Check EFLAGS.ZF from 'test VMX_RUN_VMRESUME' above */
- jz .Lvmlaunch
+ /* Clobbers EFLAGS.ZF */
+ CLEAR_CPU_BUFFERS
+
+ /* Check EFLAGS.CF from the VMX_RUN_VMRESUME bit test above. */
+ jnc .Lvmlaunch
/*
* After a successful VMRESUME/VMLAUNCH, control flow "magically"
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 94082169bb..856eef56b3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -387,7 +387,16 @@ static __always_inline void vmx_enable_fb_clear(struct vcpu_vmx *vmx)
static void vmx_update_fb_clear_dis(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
{
- vmx->disable_fb_clear = (host_arch_capabilities & ARCH_CAP_FB_CLEAR_CTRL) &&
+ /*
+ * Disable VERW's behavior of clearing CPU buffers for the guest if the
+ * CPU isn't affected by MDS/TAA, and the host hasn't forcefully enabled
+ * the mitigation. Disabling the clearing behavior provides a
+ * performance boost for guests that aren't aware that manually clearing
+ * CPU buffers is unnecessary, at the cost of MSR accesses on VM-Entry
+ * and VM-Exit.
+ */
+ vmx->disable_fb_clear = !cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF) &&
+ (host_arch_capabilities & ARCH_CAP_FB_CLEAR_CTRL) &&
!boot_cpu_has_bug(X86_BUG_MDS) &&
!boot_cpu_has_bug(X86_BUG_TAA);
@@ -7226,11 +7235,14 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
guest_state_enter_irqoff();
- /* L1D Flush includes CPU buffer clear to mitigate MDS */
+ /*
+ * L1D Flush includes CPU buffer clear to mitigate MDS, but VERW
+ * mitigation for MDS is done late in VMentry and is still
+ * executed in spite of L1D Flush. This is because an extra VERW
+ * should not matter much after the big hammer L1D Flush.
+ */
if (static_branch_unlikely(&vmx_l1d_should_flush))
vmx_l1d_flush(vcpu);
- else if (static_branch_unlikely(&mds_user_clear))
- mds_clear_cpu_buffers();
else if (static_branch_unlikely(&mmio_stale_data_clear) &&
kvm_arch_has_assigned_device(vcpu->kvm))
mds_clear_cpu_buffers();