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From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: [PATCH v3 3/4] x86: limit issuing of IBPB during context switch
Date: Wed, 25 Jan 2023 16:26:39 +0100	[thread overview]
Message-ID: <c39faba2-1ab6-71da-f748-1545aac8290b@suse.com> (raw)
In-Reply-To: <930254a6-d0c8-4910-982a-bfd227187240@suse.com>

When the outgoing vCPU had IBPB issued upon entering Xen there's no
need for a 2nd barrier during context switch.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v3: Fold into series.

--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -2015,7 +2015,8 @@ void context_switch(struct vcpu *prev, s
 
         ctxt_switch_levelling(next);
 
-        if ( opt_ibpb_ctxt_switch && !is_idle_domain(nextd) )
+        if ( opt_ibpb_ctxt_switch && !is_idle_domain(nextd) &&
+             !(prevd->arch.spec_ctrl_flags & SCF_entry_ibpb) )
         {
             static DEFINE_PER_CPU(unsigned int, last);
             unsigned int *last_id = &this_cpu(last);



  parent reply	other threads:[~2023-01-25 15:27 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-25 15:24 [PATCH v3 0/4] x86/spec-ctrl: IPBP improvements Jan Beulich
2023-01-25 15:25 ` [PATCH v3 1/4] x86/spec-ctrl: add logic to issue IBPB on exit to guest Jan Beulich
2023-01-25 21:10   ` Andrew Cooper
2023-01-26  8:02     ` Jan Beulich
2023-01-26 20:27       ` Andrew Cooper
2023-02-06 13:58         ` Jan Beulich
2023-01-25 15:26 ` [PATCH v3 2/4] x86/spec-ctrl: defer context-switch IBPB until guest entry Jan Beulich
2023-01-26 20:43   ` Andrew Cooper
2023-02-06 14:24     ` Jan Beulich
2023-01-25 15:26 ` Jan Beulich [this message]
2023-01-26 20:49   ` [PATCH v3 3/4] x86: limit issuing of IBPB during context switch Andrew Cooper
2023-01-27  7:51     ` Jan Beulich
2023-01-27 17:47       ` Andrew Cooper
2023-02-06 14:58         ` Jan Beulich
2023-01-25 15:27 ` [PATCH v3 4/4] x86/PV: issue branch prediction barrier when switching 64-bit guest to kernel mode Jan Beulich
2023-01-25 17:49 ` [PATCH v3 0/4] x86/spec-ctrl: IPBP improvements Andrew Cooper
2023-01-26  7:32   ` Jan Beulich

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