[PATCH 5.15 63/89] x86/speculation: Remove x86_spec_ctrl_mask

Greg Kroah-Hartman
2022-07-22T09:27:50Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit acac5e98ef8d638a411cfa2ee676c87e1973f126 upstream.

This mask has been made redundant by kvm_spec_ctrl_test_value(). And it
doesn't even work when MSR interception is disabled, as the guest can
just write to SPEC_CTRL directly.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/cpu/bugs.c | 31 +------------------------------
1 file changed, 1 insertion(+), 30 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -86,12 +86,6 @@ u64 spec_ctrl_current(void)
EXPORT_SYMBOL_GPL(spec_ctrl_current);

/*
- * The vendor and possibly platform specific bits which can be modified in
- * x86_spec_ctrl_base.
- */
-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_ssbd_mask is initialized in identify_boot_cpu().
*/
@@ -146,10 +140,6 @@ void __init check_bugs(void)
if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);

- /* Allow STIBP in MSR_SPEC_CTRL if supported */
- if (boot_cpu_has(X86_FEATURE_STIBP))
- x86_spec_ctrl_mask |= SPEC_CTRL_STIBP;
-
/* Select the proper CPU mitigations before patching alternatives: */
spectre_v1_select_mitigation();
spectre_v2_select_mitigation();
@@ -208,19 +198,10 @@ void __init check_bugs(void)
void
x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
{
- u64 msrval, guestval, hostval = spec_ctrl_current();
+ u64 msrval, guestval = guest_spec_ctrl, hostval = spec_ctrl_current();
struct thread_info *ti = current_thread_info();

- /* Is MSR_SPEC_CTRL implemented ? */
if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
- /*
- * Restrict guest_spec_ctrl to supported values. Clear the
- * modifiable bits in the host base value and or the
- * modifiable bits from the guest value.
- */
- guestval = hostval & ~x86_spec_ctrl_mask;
- guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;
-
if (hostval != guestval) {
msrval = setguest ? guestval : hostval;
wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
@@ -1659,16 +1640,6 @@ static enum ssb_mitigation __init __ssb_
}

/*
- * If SSBD is controlled by the SPEC_CTRL MSR, then set the proper
- * bit in the mask to allow guests to use the mitigation even in the
- * case where the host does not enable it.
- */
- if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
- static_cpu_has(X86_FEATURE_AMD_SSBD)) {
- x86_spec_ctrl_mask |= SPEC_CTRL_SSBD;
- }
-
- /*
* We have three CPU feature flags that are in play here:
* - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
* - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass