linux-kernel - [RFC PATCH 70/73] x86/pvm: Don't use SWAPGS for gsbase read/write

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Date: Mon, 26 Feb 2024 22:36:27 +0800
From: Lai Jiangshan <jiangshanlai@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Hou Wenlong <houwenlong.hwl@...group.com>,
	Lai Jiangshan <jiangshan.ljs@...group.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Ingo Molnar <mingo@...hat.com>,
	kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	x86@...nel.org,
	Kees Cook <keescook@...omium.org>,
	Juergen Gross <jgross@...e.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mike Rapoport <rppt@...nel.org>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: [RFC PATCH 70/73] x86/pvm: Don't use SWAPGS for gsbase read/write

From: Hou Wenlong <houwenlong.hwl@...group.com>

On PVM guest, SWAPGS doesn't work. So let __rdgsbase_inactive() and
__wrgsbase_inactive() to use rdmsrl()/wrmsrl() on PVM guest.

Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
---
 arch/x86/kernel/process_64.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 33b268747bb7..9a56bcef515e 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -157,7 +157,7 @@ enum which_selector {
  * traced or probed than any access to a per CPU variable happens with
  * the wrong GS.
  *
- * It is not used on Xen paravirt. When paravirt support is needed, it
+ * It is not used on Xen/PVM paravirt. When paravirt support is needed, it
  * needs to be renamed with native_ prefix.
  */
 static noinstr unsigned long __rdgsbase_inactive(void)
@@ -166,7 +166,8 @@ static noinstr unsigned long __rdgsbase_inactive(void)
 
 	lockdep_assert_irqs_disabled();
 
-	if (!cpu_feature_enabled(X86_FEATURE_XENPV)) {
+	if (!cpu_feature_enabled(X86_FEATURE_XENPV) &&
+	    !cpu_feature_enabled(X86_FEATURE_KVM_PVM_GUEST)) {
 		native_swapgs();
 		gsbase = rdgsbase();
 		native_swapgs();
@@ -184,14 +185,15 @@ static noinstr unsigned long __rdgsbase_inactive(void)
  * traced or probed than any access to a per CPU variable happens with
  * the wrong GS.
  *
- * It is not used on Xen paravirt. When paravirt support is needed, it
+ * It is not used on Xen/PVM paravirt. When paravirt support is needed, it
  * needs to be renamed with native_ prefix.
  */
 static noinstr void __wrgsbase_inactive(unsigned long gsbase)
 {
 	lockdep_assert_irqs_disabled();
 
-	if (!cpu_feature_enabled(X86_FEATURE_XENPV)) {
+	if (!cpu_feature_enabled(X86_FEATURE_XENPV) &&
+	    !cpu_feature_enabled(X86_FEATURE_KVM_PVM_GUEST)) {
 		native_swapgs();
 		wrgsbase(gsbase);
 		native_swapgs();
-- 
2.19.1.6.gb485710b