linux-kernel - [PATCH 5.10 115/130] x86/speculation: Use cached host SPEC

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Message-Id: <20220712183251.768172760@linuxfoundation.org>
Date:   Tue, 12 Jul 2022 20:39:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Ben Hutchings <ben@...adent.org.uk>
Subject: [PATCH 5.10 115/130] x86/speculation: Use cached host SPEC_CTRL value for guest entry/exit

From: Josh Poimboeuf <jpoimboe@...nel.org>

commit bbb69e8bee1bd882784947095ffb2bfe0f7c9470 upstream.

There's no need to recalculate the host value for every entry/exit.
Just use the cached value in spec_ctrl_current().

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/cpu/bugs.c |   12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -199,7 +199,7 @@ 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 = x86_spec_ctrl_base;
+	u64 msrval, guestval, hostval = spec_ctrl_current();
 	struct thread_info *ti = current_thread_info();
 
 	/* Is MSR_SPEC_CTRL implemented ? */
@@ -212,15 +212,6 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl,
 		guestval = hostval & ~x86_spec_ctrl_mask;
 		guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;
 
-		/* SSBD controlled in MSR_SPEC_CTRL */
-		if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
-		    static_cpu_has(X86_FEATURE_AMD_SSBD))
-			hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
-
-		/* Conditional STIBP enabled? */
-		if (static_branch_unlikely(&switch_to_cond_stibp))
-			hostval |= stibp_tif_to_spec_ctrl(ti->flags);
-
 		if (hostval != guestval) {
 			msrval = setguest ? guestval : hostval;
 			wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
@@ -1353,7 +1344,6 @@ static void __init spectre_v2_select_mit
 		pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);
 
 	if (spectre_v2_in_ibrs_mode(mode)) {
-		/* Force it so VMEXIT will restore correctly */
 		x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
 		write_spec_ctrl_current(x86_spec_ctrl_base, true);
 	}