[PATCH 5.4 23/37] x86/speculation: Remove x86_spec_ctrl_mask

From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
To: stable@vger.kernel.org
Cc: x86@kernel.org, kvm@vger.kernel.org, bp@alien8.de,
	pbonzini@redhat.com, peterz@infradead.org, jpoimboe@kernel.org
Subject: [PATCH 5.4 23/37] x86/speculation: Remove x86_spec_ctrl_mask
Date: Mon,  3 Oct 2022 10:10:24 -0300	[thread overview]
Message-ID: <20221003131038.12645-24-cascardo@canonical.com> (raw)
In-Reply-To: <20221003131038.12645-1-cascardo@canonical.com>

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>
---
 arch/x86/kernel/cpu/bugs.c | 31 +------------------------------
 1 file changed, 1 insertion(+), 30 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 9176a0bde0ed..7198ae236a20 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -83,12 +83,6 @@ 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().
@@ -137,10 +131,6 @@ 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();
@@ -198,19 +188,10 @@ 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);
@@ -1542,16 +1523,6 @@ 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.
-- 
2.34.1

