[PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
From: Joerg Roedel
Warn the user in case the performance can be significantly
improved by switching to a 64-bit kernel.
Suggested-by: Andy Lutomirski
Signed-off-by: Joerg Roedel
---
arch/x86/mm/pti.c | 22 ++
1 file changed, 22 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b879ccd..be8d2cd 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -517,6 +517,28 @@ void __init pti_init(void)
pr_info("enabled\n");
+#ifdef CONFIG_X86_32
+ /*
+* We check for X86_FEATURE_PCID here. But the init-code will
+* clear the feature flag on 32 bit because the feature is not
+* supported on 32 bit anyway. To print the warning we need to
+* check with cpuid directly again.
+*/
+ if (cpuid_ecx(0x1) && BIT(17)) {
+ /* Use printk to work around pr_fmt() */
+ printk(KERN_WARNING "\n");
+ printk(KERN_WARNING
"\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit
PCID-capable CPU. **\n");
+ printk(KERN_WARNING "** Your performance will increase
dramatically if you **\n");
+ printk(KERN_WARNING "** switch to a 64-bit kernel!
**\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING
"\n");
+ }
+#endif
+
pti_clone_user_shared();
/* Undo all global bits from the init pagetables in head_64.S: */
--
2.7.4
[PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
From: Joerg Roedel
Warn the user in case the performance can be significantly
improved by switching to a 64-bit kernel.
Suggested-by: Andy Lutomirski
Signed-off-by: Joerg Roedel
---
arch/x86/mm/pti.c | 22 ++
1 file changed, 22 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b879ccd..be8d2cd 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -517,6 +517,28 @@ void __init pti_init(void)
pr_info("enabled\n");
+#ifdef CONFIG_X86_32
+ /*
+* We check for X86_FEATURE_PCID here. But the init-code will
+* clear the feature flag on 32 bit because the feature is not
+* supported on 32 bit anyway. To print the warning we need to
+* check with cpuid directly again.
+*/
+ if (cpuid_ecx(0x1) && BIT(17)) {
+ /* Use printk to work around pr_fmt() */
+ printk(KERN_WARNING "\n");
+ printk(KERN_WARNING
"\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit
PCID-capable CPU. **\n");
+ printk(KERN_WARNING "** Your performance will increase
dramatically if you **\n");
+ printk(KERN_WARNING "** switch to a 64-bit kernel!
**\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING
"\n");
+ }
+#endif
+
pti_clone_user_shared();
/* Undo all global bits from the init pagetables in head_64.S: */
--
2.7.4
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Fri, Jul 13, 2018 at 11:59:44AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> > From: Joerg Roedel
> >
> > Warn the user in case the performance can be significantly
> > improved by switching to a 64-bit kernel.
>
> ...
>
> > +#ifdef CONFIG_X86_32
> > + if (boot_cpu_has(X86_FEATURE_PCID)) {
>
> I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
> early_identify_cpu() prevent this from working?
Right you are, I don't have a PCID capable system at hand for testing,
so I didn't catch this...
> Boris, do we have a straightforward way to ask "does the CPU advertise
> this feature in CPUID regardless of whether we have it enabled right
> now"?
I guess we need to call cpuid again.
Regards,
Joerg
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Fri, Jul 13, 2018 at 11:59:44AM -0700, Andy Lutomirski wrote:
> On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> > From: Joerg Roedel
> >
> > Warn the user in case the performance can be significantly
> > improved by switching to a 64-bit kernel.
>
> ...
>
> > +#ifdef CONFIG_X86_32
> > + if (boot_cpu_has(X86_FEATURE_PCID)) {
>
> I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
> early_identify_cpu() prevent this from working?
Right you are, I don't have a PCID capable system at hand for testing,
so I didn't catch this...
> Boris, do we have a straightforward way to ask "does the CPU advertise
> this feature in CPUID regardless of whether we have it enabled right
> now"?
I guess we need to call cpuid again.
Regards,
Joerg
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> From: Joerg Roedel
>
> Warn the user in case the performance can be significantly
> improved by switching to a 64-bit kernel.
...
> +#ifdef CONFIG_X86_32
> + if (boot_cpu_has(X86_FEATURE_PCID)) {
I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
early_identify_cpu() prevent this from working?
Boris, do we have a straightforward way to ask "does the CPU advertise
this feature in CPUID regardless of whether we have it enabled right
now"?
--Andy
Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel wrote:
> From: Joerg Roedel
>
> Warn the user in case the performance can be significantly
> improved by switching to a 64-bit kernel.
...
> +#ifdef CONFIG_X86_32
> + if (boot_cpu_has(X86_FEATURE_PCID)) {
I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
early_identify_cpu() prevent this from working?
Boris, do we have a straightforward way to ask "does the CPU advertise
this feature in CPUID regardless of whether we have it enabled right
now"?
--Andy
[PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
From: Joerg Roedel
Warn the user in case the performance can be significantly
improved by switching to a 64-bit kernel.
Suggested-by: Andy Lutomirski
Signed-off-by: Joerg Roedel
---
arch/x86/mm/pti.c | 16
1 file changed, 16 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b879ccd..e20283fa 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -517,6 +517,22 @@ void __init pti_init(void)
pr_info("enabled\n");
+#ifdef CONFIG_X86_32
+ if (boot_cpu_has(X86_FEATURE_PCID)) {
+ /* Use printk to work around pr_fmt() */
+ printk(KERN_WARNING "\n");
+ printk(KERN_WARNING
"\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit
PCID-capable CPU. **\n");
+ printk(KERN_WARNING "** Your performance will increase
dramatically if you **\n");
+ printk(KERN_WARNING "** switch to a 64-bit kernel!
**\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING
"\n");
+ }
+#endif
+
pti_clone_user_shared();
/* Undo all global bits from the init pagetables in head_64.S: */
--
2.7.4
[PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU
From: Joerg Roedel
Warn the user in case the performance can be significantly
improved by switching to a 64-bit kernel.
Suggested-by: Andy Lutomirski
Signed-off-by: Joerg Roedel
---
arch/x86/mm/pti.c | 16
1 file changed, 16 insertions(+)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b879ccd..e20283fa 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -517,6 +517,22 @@ void __init pti_init(void)
pr_info("enabled\n");
+#ifdef CONFIG_X86_32
+ if (boot_cpu_has(X86_FEATURE_PCID)) {
+ /* Use printk to work around pr_fmt() */
+ printk(KERN_WARNING "\n");
+ printk(KERN_WARNING
"\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit
PCID-capable CPU. **\n");
+ printk(KERN_WARNING "** Your performance will increase
dramatically if you **\n");
+ printk(KERN_WARNING "** switch to a 64-bit kernel!
**\n");
+ printk(KERN_WARNING "**
**\n");
+ printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING!
WARNING! WARNING! **\n");
+ printk(KERN_WARNING
"\n");
+ }
+#endif
+
pti_clone_user_shared();
/* Undo all global bits from the init pagetables in head_64.S: */
--
2.7.4
