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x86/speculation: Remove x86_spec_ctrl_mask

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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>
This commit is contained in:
Josh Poimboeuf 2022-06-17 12:12:48 -07:00 committed by Borislav Petkov
parent bbb69e8bee
commit acac5e98ef
1 changed files with 1 additions and 30 deletions
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31
arch/x86/kernel/cpu/bugs.c
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@ -85,12 +85,6 @@ 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);
@ -1665,16 +1646,6 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
break;
}
/*
* 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.