On 7/14/18 7:15 AM, Juergen Gross wrote:
> On 14/07/18 11:33, Srivatsa S. Bhat wrote:
>> From: David Woodhouse <dwmw@xxxxxxxxxxxx>
>>
>> commit def9331a12977770cc6132d79f8e6565871e8e38 upstream
>>
>> 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@xxxxxxxx>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>> Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>> Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
>> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx>
>> Reviewed-by: Matt Helsley (VMware) <matt.helsley@xxxxxxxxx>
>> Reviewed-by: Alexey Makhalov <amakhalov@xxxxxxxxxx>
>> Reviewed-by: Bo Gan <ganb@xxxxxxxxxx>
>
> I believe you'll need upstream commit
> 60d3450167433f2d099ce2869dc52dd9e7dc9b29 ("x86/cpu: Re-apply forced caps
> every time CPU caps are re-read") for this patch to work as intended.
>
> It was necessary for 4.9, at least.
>
Ah, I see. Thank you for letting me know, Juergen! Looking at 4.9.112,
I see that in addition to the patch you mentioned above, we should
also backport this patch to 4.4: upstream commit 74899d92e66663dc7671a
x6/xen: Add call of speculative_store_bypass_ht_init() to PV paths
The 4.9 backports of these patches apply cleanly to 4.4 as well, but I
have attached them anyway with this mail. Greg, could you consider
queuing these 2 patches for 4.4 at the end of this patch series?
1. x86/xen: Add call of speculative_store_bypass_ht_init() to PV paths
2. x86/cpu: Re-apply forced caps every time CPU caps are re-read
Thank you!
Regards,
Srivatsa
VMware Photon OS
From 9dee2b7c4d4868423d9812c969b0b724fdf780c6 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@xxxxxxxx>
Date: Thu, 21 Jun 2018 10:43:31 +0200
Subject: [PATCH 1/2] x86/xen: Add call of speculative_store_bypass_ht_init()
to PV paths
commit 74899d92e66663dc7671a8017b3146dcd4735f3b upstream.
Commit:
1f50ddb4f418 ("x86/speculation: Handle HT correctly on AMD")
... added speculative_store_bypass_ht_init() to the per-CPU initialization sequence.
speculative_store_bypass_ht_init() needs to be called on each CPU for
PV guests, too.
Reported-by: Brian Woods <brian.woods@xxxxxxx>
Tested-by: Brian Woods <brian.woods@xxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: boris.ostrovsky@xxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Fixes: 1f50ddb4f4189243c05926b842dc1a0332195f31 ("x86/speculation: Handle HT correctly on AMD")
Link: https://lore.kernel.org/lkml/20180621084331.21228-1-jgross@xxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx>
---
arch/x86/xen/smp.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 3f4ebf0..29e50d1 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -28,6 +28,7 @@
#include <xen/interface/vcpu.h>
#include <xen/interface/xenpmu.h>
+#include <asm/spec-ctrl.h>
#include <asm/xen/interface.h>
#include <asm/xen/hypercall.h>
@@ -87,6 +88,8 @@ static void cpu_bringup(void)
cpu_data(cpu).x86_max_cores = 1;
set_cpu_sibling_map(cpu);
+ speculative_store_bypass_ht_init();
+
xen_setup_cpu_clockevents();
notify_cpu_starting(cpu);
@@ -357,6 +360,8 @@ static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
}
set_cpu_sibling_map(0);
+ speculative_store_bypass_ht_init();
+
xen_pmu_init(0);
if (xen_smp_intr_init(0))
--
2.7.4
From bdda88b5f410398f03ec6bb294cce07173232ea8 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@xxxxxxxxxx>
Date: Wed, 18 Jan 2017 11:15:39 -0800
Subject: [PATCH 2/2] x86/cpu: Re-apply forced caps every time CPU caps are
re-read
commit 60d3450167433f2d099ce2869dc52dd9e7dc9b29 upstream.
Calling get_cpu_cap() will reset a bunch of CPU features. This will
cause the system to lose track of force-set and force-cleared
features in the words that are reset until the end of CPU
initialization. This can cause X86_FEATURE_FPU, for example, to
change back and forth during boot and potentially confuse CPU setup.
To minimize the chance of confusion, re-apply forced caps every time
get_cpu_cap() is called.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Whitehead <tedheadster@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Link: http://lkml.kernel.org/r/c817eb373d2c67c2c81413a70fc9b845fa34a37e.1484705016.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa@xxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/common.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9ad38ad..3d21b28 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -803,6 +803,13 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
init_scattered_cpuid_features(c);
init_speculation_control(c);
+
+ /*
+ * Clear/Set all flags overridden by options, after probe.
+ * This needs to happen each time we re-probe, which may happen
+ * several times during CPU initialization.
+ */
+ apply_forced_caps(c);
}
static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
--
2.7.4
