[PATCH 0/3] Correct 4.9 stable commit 944e0fc51a89c98

[PATCH 0/3] Correct 4.9 stable commit 944e0fc51a89c98

[Juergen Gross]

Above commit is a wrong backport, as it is based on a missing
prerequisite patch. Correct that by reverting said commit, include the
missing patch, and do the backport correctly.

Juergen Gross (3):
  x86/amd: revert commit 944e0fc51a89c9827b98813d65dc083274777c7f
  xen: set cpu capabilities from xen_start_kernel()
  x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

 arch/x86/xen/enlighten.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

-- 
2.13.6

[PATCH 1/3] x86/amd: revert commit 944e0fc51a89c9827b9

[Juergen Gross]

Revert commit 944e0fc51a89c9827b98813d65dc083274777c7f ("x86/amd: don't
set X86_BUG_SYSRET_SS_ATTRS when running under Xen") as it is lacking
a prerequisite patch and is making things worse.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/kernel/cpu/amd.c | 5 ++---
 arch/x86/xen/enlighten.c  | 4 +++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4c2be99fa0fb..cd0abf8ed314 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,9 +857,8 @@ static void init_amd(struct cpuinfo_x86 *c)
 		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
 			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
 
-	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
-	if (!cpu_has(c, X86_FEATURE_XENPV))
-		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+	/* AMD CPUs don't reset SS attributes on SYSRET */
+	set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 081437b5f381..2bea87cc0ff2 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1977,8 +1977,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
 static void xen_set_cpu_features(struct cpuinfo_x86 *c)
 {
-	if (xen_pv_domain())
+	if (xen_pv_domain()) {
+		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 		set_cpu_cap(c, X86_FEATURE_XENPV);
+	}
 }
 
 static void xen_pin_vcpu(int cpu)
-- 
2.13.6

[PATCH 1/3] x86/amd: revert commit 944e0fc51a89c9827b9

[Juergen Gross]

Revert commit 944e0fc51a89c9827b98813d65dc083274777c7f ("x86/amd: don't
set X86_BUG_SYSRET_SS_ATTRS when running under Xen") as it is lacking
a prerequisite patch and is making things worse.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/kernel/cpu/amd.c | 5 ++---
 arch/x86/xen/enlighten.c  | 4 +++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 4c2be99fa0fb..cd0abf8ed314 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,9 +857,8 @@ static void init_amd(struct cpuinfo_x86 *c)
 		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
 			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
 
-	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
-	if (!cpu_has(c, X86_FEATURE_XENPV))
-		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+	/* AMD CPUs don't reset SS attributes on SYSRET */
+	set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 081437b5f381..2bea87cc0ff2 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1977,8 +1977,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
 static void xen_set_cpu_features(struct cpuinfo_x86 *c)
 {
-	if (xen_pv_domain())
+	if (xen_pv_domain()) {
+		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 		set_cpu_cap(c, X86_FEATURE_XENPV);
+	}
 }
 
 static void xen_pin_vcpu(int cpu)
-- 
2.13.6


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[PATCH 2/3] xen: set cpu capabilities from xen_start_kernel()

[Juergen Gross]

There is no need to set the same capabilities for each cpu
individually. This can easily be done for all cpus when starting the
kernel.

Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
cpu capabilities from xen_start_kernel()")

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/xen/enlighten.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 2bea87cc0ff2..fb1867fedd29 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -471,6 +471,14 @@ static void __init xen_init_cpuid_mask(void)
 		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
 }
 
+static void __init xen_init_capabilities(void)
+{
+	if (xen_pv_domain()) {
+		setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
+		setup_force_cpu_cap(X86_FEATURE_XENPV);
+	}
+}
+
 static void xen_set_debugreg(int reg, unsigned long val)
 {
 	HYPERVISOR_set_debugreg(reg, val);
@@ -1631,6 +1639,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
 
 	xen_init_irq_ops();
 	xen_init_cpuid_mask();
+	xen_init_capabilities();
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	/*
@@ -1975,14 +1984,6 @@ bool xen_hvm_need_lapic(void)
 }
 EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
-static void xen_set_cpu_features(struct cpuinfo_x86 *c)
-{
-	if (xen_pv_domain()) {
-		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
-		set_cpu_cap(c, X86_FEATURE_XENPV);
-	}
-}
-
 static void xen_pin_vcpu(int cpu)
 {
 	static bool disable_pinning;
@@ -2029,7 +2030,6 @@ const struct hypervisor_x86 x86_hyper_xen = {
 	.init_platform		= xen_hvm_guest_init,
 #endif
 	.x2apic_available	= xen_x2apic_para_available,
-	.set_cpu_features       = xen_set_cpu_features,
 	.pin_vcpu               = xen_pin_vcpu,
 };
 EXPORT_SYMBOL(x86_hyper_xen);
-- 
2.13.6

[PATCH 2/3] xen: set cpu capabilities from xen_start_kernel()

[Juergen Gross]

There is no need to set the same capabilities for each cpu
individually. This can easily be done for all cpus when starting the
kernel.

Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
cpu capabilities from xen_start_kernel()")

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/xen/enlighten.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 2bea87cc0ff2..fb1867fedd29 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -471,6 +471,14 @@ static void __init xen_init_cpuid_mask(void)
 		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
 }
 
+static void __init xen_init_capabilities(void)
+{
+	if (xen_pv_domain()) {
+		setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
+		setup_force_cpu_cap(X86_FEATURE_XENPV);
+	}
+}
+
 static void xen_set_debugreg(int reg, unsigned long val)
 {
 	HYPERVISOR_set_debugreg(reg, val);
@@ -1631,6 +1639,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
 
 	xen_init_irq_ops();
 	xen_init_cpuid_mask();
+	xen_init_capabilities();
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	/*
@@ -1975,14 +1984,6 @@ bool xen_hvm_need_lapic(void)
 }
 EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
-static void xen_set_cpu_features(struct cpuinfo_x86 *c)
-{
-	if (xen_pv_domain()) {
-		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
-		set_cpu_cap(c, X86_FEATURE_XENPV);
-	}
-}
-
 static void xen_pin_vcpu(int cpu)
 {
 	static bool disable_pinning;
@@ -2029,7 +2030,6 @@ const struct hypervisor_x86 x86_hyper_xen = {
 	.init_platform		= xen_hvm_guest_init,
 #endif
 	.x2apic_available	= xen_x2apic_para_available,
-	.set_cpu_features       = xen_set_cpu_features,
 	.pin_vcpu               = xen_pin_vcpu,
 };
 EXPORT_SYMBOL(x86_hyper_xen);
-- 
2.13.6


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[PATCH 3/3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

[Juergen Gross]

When running as Xen pv guest X86_BUG_SYSRET_SS_ATTRS must not be set
on AMD cpus.

This bug/feature bit is kind of special as it will be used very early
when switching threads. Setting the bit and clearing it a little bit
later leaves a critical window where things can go wrong. This time
window has enlarged a little bit by using setup_clear_cpu_cap() instead
of the hypervisor's set_cpu_features callback. It seems this larger
window now makes it rather easy to hit the problem.

The proper solution is to never set the bit in case of Xen.

Upstream commit: def9331a12977770cc6132d79f8e6565871e8e38 ("x86/amd:
don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen")

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/amd.c | 5 +++--
 arch/x86/xen/enlighten.c  | 4 +---
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index cd0abf8ed314..4c2be99fa0fb 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,8 +857,9 @@ static void init_amd(struct cpuinfo_x86 *c)
 		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
 			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
 
-	/* AMD CPUs don't reset SS attributes on SYSRET */
-	set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
+	if (!cpu_has(c, X86_FEATURE_XENPV))
+		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index fb1867fedd29..a11b46f1abbd 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -473,10 +473,8 @@ static void __init xen_init_cpuid_mask(void)
 
 static void __init xen_init_capabilities(void)
 {
-	if (xen_pv_domain()) {
-		setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
+	if (xen_pv_domain())
 		setup_force_cpu_cap(X86_FEATURE_XENPV);
-	}
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)
-- 
2.13.6

[PATCH 3/3] x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

[Juergen Gross]

When running as Xen pv guest X86_BUG_SYSRET_SS_ATTRS must not be set
on AMD cpus.

This bug/feature bit is kind of special as it will be used very early
when switching threads. Setting the bit and clearing it a little bit
later leaves a critical window where things can go wrong. This time
window has enlarged a little bit by using setup_clear_cpu_cap() instead
of the hypervisor's set_cpu_features callback. It seems this larger
window now makes it rather easy to hit the problem.

The proper solution is to never set the bit in case of Xen.

Upstream commit: def9331a12977770cc6132d79f8e6565871e8e38 ("x86/amd:
don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen")

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/amd.c | 5 +++--
 arch/x86/xen/enlighten.c  | 4 +---
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index cd0abf8ed314..4c2be99fa0fb 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,8 +857,9 @@ static void init_amd(struct cpuinfo_x86 *c)
 		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
 			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
 
-	/* AMD CPUs don't reset SS attributes on SYSRET */
-	set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
+	if (!cpu_has(c, X86_FEATURE_XENPV))
+		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 }
 
 #ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index fb1867fedd29..a11b46f1abbd 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -473,10 +473,8 @@ static void __init xen_init_cpuid_mask(void)
 
 static void __init xen_init_capabilities(void)
 {
-	if (xen_pv_domain()) {
-		setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
+	if (xen_pv_domain())
 		setup_force_cpu_cap(X86_FEATURE_XENPV);
-	}
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)
-- 
2.13.6


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Re: [PATCH 0/3] Correct 4.9 stable commit 944e0fc51a89c98

[Greg KH]

On Wed, May 30, 2018 at 01:09:55PM +0200, Juergen Gross wrote:
> Above commit is a wrong backport, as it is based on a missing
> prerequisite patch. Correct that by reverting said commit, include the
> missing patch, and do the backport correctly.
> 
> Juergen Gross (3):
>   x86/amd: revert commit 944e0fc51a89c9827b98813d65dc083274777c7f
>   xen: set cpu capabilities from xen_start_kernel()
>   x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

All now queued up, thanks.

greg k-h

Re: [PATCH 0/3] Correct 4.9 stable commit 944e0fc51a89c98

[Greg KH]

On Wed, May 30, 2018 at 01:09:55PM +0200, Juergen Gross wrote:
> Above commit is a wrong backport, as it is based on a missing
> prerequisite patch. Correct that by reverting said commit, include the
> missing patch, and do the backport correctly.
> 
> Juergen Gross (3):
>   x86/amd: revert commit 944e0fc51a89c9827b98813d65dc083274777c7f
>   xen: set cpu capabilities from xen_start_kernel()
>   x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

All now queued up, thanks.

greg k-h

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Patch "x86/amd: revert commit 944e0fc51a89c9827b9" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/amd: revert commit 944e0fc51a89c9827b9

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-amd-revert-commit-944e0fc51a89c9827b9.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From foo@baz Sat Jun  2 15:10:07 CEST 2018
From: Juergen Gross <jgross@suse.com>
Date: Wed, 30 May 2018 13:09:56 +0200
Subject: x86/amd: revert commit 944e0fc51a89c9827b9
To: stable@vger.kernel.org, xen-devel@lists.xenproject.org
Cc: dwmw@amazon.co.uk, boris.ostrovsky@oracle.com, Juergen Gross <jgross@suse.com>
Message-ID: <20180530110958.19413-2-jgross@suse.com>

From: Juergen Gross <jgross@suse.com>

Revert commit 944e0fc51a89c9827b98813d65dc083274777c7f ("x86/amd: don't
set X86_BUG_SYSRET_SS_ATTRS when running under Xen") as it is lacking
a prerequisite patch and is making things worse.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/cpu/amd.c |    5 ++---
 arch/x86/xen/enlighten.c  |    4 +++-
 2 files changed, 5 insertions(+), 4 deletions(-)

--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,9 +857,8 @@ static void init_amd(struct cpuinfo_x86
 		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
 			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
 
-	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
-	if (!cpu_has(c, X86_FEATURE_XENPV))
-		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+	/* AMD CPUs don't reset SS attributes on SYSRET */
+	set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 }
 
 #ifdef CONFIG_X86_32
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1977,8 +1977,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
 static void xen_set_cpu_features(struct cpuinfo_x86 *c)
 {
-	if (xen_pv_domain())
+	if (xen_pv_domain()) {
+		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 		set_cpu_cap(c, X86_FEATURE_XENPV);
+	}
 }
 
 static void xen_pin_vcpu(int cpu)


Patches currently in stable-queue which might be from jgross@suse.com are

queue-4.9/x86-amd-don-t-set-x86_bug_sysret_ss_attrs-when-running-under-xen.patch
queue-4.9/x86-amd-revert-commit-944e0fc51a89c9827b9.patch
queue-4.9/xen-set-cpu-capabilities-from-xen_start_kernel.patch

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Patch "xen: set cpu capabilities from xen_start_kernel()" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    xen: set cpu capabilities from xen_start_kernel()

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xen-set-cpu-capabilities-from-xen_start_kernel.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From foo@baz Sat Jun  2 15:10:07 CEST 2018
From: Juergen Gross <jgross@suse.com>
Date: Wed, 30 May 2018 13:09:57 +0200
Subject: xen: set cpu capabilities from xen_start_kernel()
To: stable@vger.kernel.org, xen-devel@lists.xenproject.org
Cc: dwmw@amazon.co.uk, boris.ostrovsky@oracle.com, Juergen Gross <jgross@suse.com>
Message-ID: <20180530110958.19413-3-jgross@suse.com>

From: Juergen Gross <jgross@suse.com>

Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
cpu capabilities from xen_start_kernel()")

There is no need to set the same capabilities for each cpu
individually. This can easily be done for all cpus when starting the
kernel.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/xen/enlighten.c |   18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -471,6 +471,14 @@ static void __init xen_init_cpuid_mask(v
 		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
 }
 
+static void __init xen_init_capabilities(void)
+{
+	if (xen_pv_domain()) {
+		setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
+		setup_force_cpu_cap(X86_FEATURE_XENPV);
+	}
+}
+
 static void xen_set_debugreg(int reg, unsigned long val)
 {
 	HYPERVISOR_set_debugreg(reg, val);
@@ -1631,6 +1639,7 @@ asmlinkage __visible void __init xen_sta
 
 	xen_init_irq_ops();
 	xen_init_cpuid_mask();
+	xen_init_capabilities();
 
 #ifdef CONFIG_X86_LOCAL_APIC
 	/*
@@ -1975,14 +1984,6 @@ bool xen_hvm_need_lapic(void)
 }
 EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
-static void xen_set_cpu_features(struct cpuinfo_x86 *c)
-{
-	if (xen_pv_domain()) {
-		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
-		set_cpu_cap(c, X86_FEATURE_XENPV);
-	}
-}
-
 static void xen_pin_vcpu(int cpu)
 {
 	static bool disable_pinning;
@@ -2029,7 +2030,6 @@ const struct hypervisor_x86 x86_hyper_xe
 	.init_platform		= xen_hvm_guest_init,
 #endif
 	.x2apic_available	= xen_x2apic_para_available,
-	.set_cpu_features       = xen_set_cpu_features,
 	.pin_vcpu               = xen_pin_vcpu,
 };
 EXPORT_SYMBOL(x86_hyper_xen);


Patches currently in stable-queue which might be from jgross@suse.com are

queue-4.9/x86-amd-don-t-set-x86_bug_sysret_ss_attrs-when-running-under-xen.patch
queue-4.9/x86-amd-revert-commit-944e0fc51a89c9827b9.patch
queue-4.9/xen-set-cpu-capabilities-from-xen_start_kernel.patch

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Patch "x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-amd-don-t-set-x86_bug_sysret_ss_attrs-when-running-under-xen.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From foo@baz Sat Jun  2 15:10:07 CEST 2018
From: Juergen Gross <jgross@suse.com>
Date: Wed, 30 May 2018 13:09:58 +0200
Subject: x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen
To: stable@vger.kernel.org, xen-devel@lists.xenproject.org
Cc: dwmw@amazon.co.uk, boris.ostrovsky@oracle.com, Juergen Gross <jgross@suse.com>
Message-ID: <20180530110958.19413-4-jgross@suse.com>

From: Juergen Gross <jgross@suse.com>

Upstream commit: def9331a12977770cc6132d79f8e6565871e8e38 ("x86/amd:
don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen")

When running as Xen pv guest X86_BUG_SYSRET_SS_ATTRS must not be set
on AMD cpus.

This bug/feature bit is kind of special as it will be used very early
when switching threads. Setting the bit and clearing it a little bit
later leaves a critical window where things can go wrong. This time
window has enlarged a little bit by using setup_clear_cpu_cap() instead
of the hypervisor's set_cpu_features callback. It seems this larger
window now makes it rather easy to hit the problem.

The proper solution is to never set the bit in case of Xen.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kernel/cpu/amd.c |    5 +++--
 arch/x86/xen/enlighten.c  |    4 +---
 2 files changed, 4 insertions(+), 5 deletions(-)

--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -857,8 +857,9 @@ static void init_amd(struct cpuinfo_x86
 		if (cpu_has(c, X86_FEATURE_3DNOW) || cpu_has(c, X86_FEATURE_LM))
 			set_cpu_cap(c, X86_FEATURE_3DNOWPREFETCH);
 
-	/* AMD CPUs don't reset SS attributes on SYSRET */
-	set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+	/* AMD CPUs don't reset SS attributes on SYSRET, Xen does. */
+	if (!cpu_has(c, X86_FEATURE_XENPV))
+		set_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
 }
 
 #ifdef CONFIG_X86_32
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -473,10 +473,8 @@ static void __init xen_init_cpuid_mask(v
 
 static void __init xen_init_capabilities(void)
 {
-	if (xen_pv_domain()) {
-		setup_clear_cpu_cap(X86_BUG_SYSRET_SS_ATTRS);
+	if (xen_pv_domain())
 		setup_force_cpu_cap(X86_FEATURE_XENPV);
-	}
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)


Patches currently in stable-queue which might be from jgross@suse.com are

queue-4.9/x86-amd-don-t-set-x86_bug_sysret_ss_attrs-when-running-under-xen.patch
queue-4.9/x86-amd-revert-commit-944e0fc51a89c9827b9.patch
queue-4.9/xen-set-cpu-capabilities-from-xen_start_kernel.patch

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Re: [PATCH 2/3] xen: set cpu capabilities from xen_start_kernel()

[Woodhouse, David]

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On Wed, 2018-05-30 at 13:09 +0200, Juergen Gross wrote:
> There is no need to set the same capabilities for each cpu
> individually. This can easily be done for all cpus when starting the
> kernel.
> 
> Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
> cpu capabilities from xen_start_kernel()")
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

That breaks PV guests because they get KAISER enabled — when
kaiser_check_boottime_disable() runs, X86_FEATURE_XENPV isn't set.

Simon is testing, and about to send a fix...

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Re: [PATCH 2/3] xen: set cpu capabilities from xen_start_kernel()

[Juergen Gross]

On 11/07/18 11:15, Woodhouse, David wrote:
> On Wed, 2018-05-30 at 13:09 +0200, Juergen Gross wrote:
>> There is no need to set the same capabilities for each cpu
>> individually. This can easily be done for all cpus when starting the
>> kernel.
>>
>> Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
>> cpu capabilities from xen_start_kernel()")
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> 
> That breaks PV guests because they get KAISER enabled — when
> kaiser_check_boottime_disable() runs, X86_FEATURE_XENPV isn't set.

Which kernel version are you talking about?

With upstream commit 60d3450167433f2d099ce2869dc52dd9e7dc9b29 which will
be part of next stable-4.9 everything is fine.


Juergen

Re: [PATCH 2/3] xen: set cpu capabilities from xen_start_kernel()

[Juergen Gross]

On 11/07/18 11:15, Woodhouse, David wrote:
> On Wed, 2018-05-30 at 13:09 +0200, Juergen Gross wrote:
>> There is no need to set the same capabilities for each cpu
>> individually. This can easily be done for all cpus when starting the
>> kernel.
>>
>> Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
>> cpu capabilities from xen_start_kernel()")
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> 
> That breaks PV guests because they get KAISER enabled — when
> kaiser_check_boottime_disable() runs, X86_FEATURE_XENPV isn't set.

Which kernel version are you talking about?

With upstream commit 60d3450167433f2d099ce2869dc52dd9e7dc9b29 which will
be part of next stable-4.9 everything is fine.


Juergen

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Re: [PATCH 2/3] xen: set cpu capabilities from xen_start_kernel()

[Woodhouse, David]

[-- Attachment #1.1: Type: text/plain, Size: 1011 bytes --]



On Wed, 2018-07-11 at 11:46 +0200, Juergen Gross wrote:
> On 11/07/18 11:15, Woodhouse, David wrote:
> > 
> > On Wed, 2018-05-30 at 13:09 +0200, Juergen Gross wrote:
> > > 
> > > There is no need to set the same capabilities for each cpu
> > > individually. This can easily be done for all cpus when starting the
> > > kernel.
> > > 
> > > Upstream commit: 0808e80cb760de2733c0527d2090ed2205a1eef8 ("xen: set
> > > cpu capabilities from xen_start_kernel()")
> > > 
> > > Signed-off-by: Juergen Gross <jgross@suse.com>
> > > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> > That breaks PV guests because they get KAISER enabled — when
> > kaiser_check_boottime_disable() runs, X86_FEATURE_XENPV isn't set.
>
> Which kernel version are you talking about?
> 
> With upstream commit 60d3450167433f2d099ce2869dc52dd9e7dc9b29 which will
> be part of next stable-4.9 everything is fine.

Right. That's what Simon had also backported. We hadn't spotted it was
already lined up.

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[PATCH 0/3] Correct 4.9 stable commit 944e0fc51a89c98

[Juergen Gross]

Above commit is a wrong backport, as it is based on a missing
prerequisite patch. Correct that by reverting said commit, include the
missing patch, and do the backport correctly.

Juergen Gross (3):
  x86/amd: revert commit 944e0fc51a89c9827b98813d65dc083274777c7f
  xen: set cpu capabilities from xen_start_kernel()
  x86/amd: don't set X86_BUG_SYSRET_SS_ATTRS when running under Xen

 arch/x86/xen/enlighten.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

-- 
2.13.6


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