* [PATCH 0/3] CR4 fixes (some are urgent)
@ 2016-09-28 19:34 Andy Lutomirski
2016-09-28 19:34 ` [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines Andy Lutomirski
` (2 more replies)
0 siblings, 3 replies; 8+ messages in thread
From: Andy Lutomirski @ 2016-09-28 19:34 UTC (permalink / raw)
To: x86; +Cc: david, Borislav Petkov, Brian Gerst, linux-kernel, Andy Lutomirski
Hi Ingo, etc:
Patches 1 and 2 fix boot regressions. Patch 1 needs to be
backported. Patch 2 doesn't because the regression is new in 4.8
(although it's probably unobservable because the regression fixed in
patch 1 also prevented bootup on affected CPUs).
Patch 3 cleans the whole mess up. It's probably not 4.8 material,
but I'm sending it as part of this series for ease of review. If
you like, you could apply patches 1 and 2 to x86/urgent, merge into
x86/asm, and apply patch 3 on top.
Andy Lutomirski (3):
x86/init: Fix cr4_init_shadow() on CR4-less machines
x86/boot: Fix another __read_cr4() case on 486
x86/asm: Get rid of __read_cr4_safe()
arch/x86/include/asm/paravirt.h | 4 ----
arch/x86/include/asm/paravirt_types.h | 1 -
arch/x86/include/asm/special_insns.h | 22 +++++++---------------
arch/x86/kernel/paravirt.c | 1 -
arch/x86/kernel/process_32.c | 2 +-
arch/x86/kernel/setup.c | 9 +++++++--
arch/x86/power/cpu.c | 2 +-
arch/x86/xen/enlighten.c | 1 -
8 files changed, 16 insertions(+), 26 deletions(-)
--
2.7.4
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines
2016-09-28 19:34 [PATCH 0/3] CR4 fixes (some are urgent) Andy Lutomirski
@ 2016-09-28 19:34 ` Andy Lutomirski
2016-09-29 11:44 ` Borislav Petkov
2016-09-29 18:21 ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
2016-09-28 19:34 ` [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486 Andy Lutomirski
2016-09-28 19:34 ` [PATCH 3/3] x86/asm: Get rid of __read_cr4_safe() Andy Lutomirski
2 siblings, 2 replies; 8+ messages in thread
From: Andy Lutomirski @ 2016-09-28 19:34 UTC (permalink / raw)
To: x86
Cc: david, Borislav Petkov, Brian Gerst, linux-kernel,
Andy Lutomirski, stable
cr4_init_shadow() will panic on 486-like machines without CR4. Fix
it using __read_cr4_safe().
Cc: stable@vger.kernel.org
Reported-by: david@saggiorato.net
Fixes: 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/include/asm/tlbflush.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 6fa85944af83..dee8a70382ba 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -81,7 +81,7 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
/* Initialize cr4 shadow for this CPU. */
static inline void cr4_init_shadow(void)
{
- this_cpu_write(cpu_tlbstate.cr4, __read_cr4());
+ this_cpu_write(cpu_tlbstate.cr4, __read_cr4_safe());
}
/* Set in this cpu's CR4. */
--
2.7.4
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486
2016-09-28 19:34 [PATCH 0/3] CR4 fixes (some are urgent) Andy Lutomirski
2016-09-28 19:34 ` [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines Andy Lutomirski
@ 2016-09-28 19:34 ` Andy Lutomirski
2016-09-29 11:48 ` Borislav Petkov
2016-09-28 19:34 ` [PATCH 3/3] x86/asm: Get rid of __read_cr4_safe() Andy Lutomirski
2 siblings, 1 reply; 8+ messages in thread
From: Andy Lutomirski @ 2016-09-28 19:34 UTC (permalink / raw)
To: x86; +Cc: david, Borislav Petkov, Brian Gerst, linux-kernel, Andy Lutomirski
The condition for reading CR4 was wrong: there are some CPUs with
CPUID but not CR4. Rather than trying to make the condition exact,
using __read_cr4_safe().
Reported-by: david@saggiorato.net
Fixes: 18bc7bd523e0 ("x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features directly")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/kernel/setup.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0fa60f5f5a16..5930a4d191b4 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1137,9 +1137,13 @@ void __init setup_arch(char **cmdline_p)
* auditing all the early-boot CR4 manipulation would be needed to
* rule it out.
*/
- if (boot_cpu_data.cpuid_level >= 0)
- /* A CPU has %cr4 if and only if it has CPUID. */
- mmu_cr4_features = __read_cr4();
+ if (boot_cpu_data.cpuid_level >= 0) {
+ /*
+ * CPUs without CPUID don't have CR4. CPUs with CPUID
+ * usually have CR4.
+ */
+ mmu_cr4_features = __read_cr4_safe();
+ }
memblock_set_current_limit(get_max_mapped());
--
2.7.4
^ permalink raw reply related [flat|nested] 8+ messages in thread
* [PATCH 3/3] x86/asm: Get rid of __read_cr4_safe()
2016-09-28 19:34 [PATCH 0/3] CR4 fixes (some are urgent) Andy Lutomirski
2016-09-28 19:34 ` [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines Andy Lutomirski
2016-09-28 19:34 ` [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486 Andy Lutomirski
@ 2016-09-28 19:34 ` Andy Lutomirski
2 siblings, 0 replies; 8+ messages in thread
From: Andy Lutomirski @ 2016-09-28 19:34 UTC (permalink / raw)
To: x86; +Cc: david, Borislav Petkov, Brian Gerst, linux-kernel, Andy Lutomirski
We use __read_cr4() vs __read_cr4_safe() inconsistently. On
CR4-less CPUs, all CR4 bits are effectively clear, so we can make
the code simpler and more robust by making __read_cr4() always fix
up faults on 32-bit kernels.
This may fix some bugs on old 486-like CPUs, but I don't have any
easy way to test that.
Cc: david@saggiorato.net
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/include/asm/paravirt.h | 4 ----
arch/x86/include/asm/paravirt_types.h | 1 -
arch/x86/include/asm/special_insns.h | 22 +++++++---------------
arch/x86/include/asm/tlbflush.h | 2 +-
arch/x86/kernel/paravirt.c | 1 -
arch/x86/kernel/process_32.c | 2 +-
arch/x86/kernel/setup.c | 5 +++--
arch/x86/power/cpu.c | 2 +-
arch/x86/xen/enlighten.c | 1 -
9 files changed, 13 insertions(+), 27 deletions(-)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 2970d22d7766..91b6f4eed3fd 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -80,10 +80,6 @@ static inline unsigned long __read_cr4(void)
{
return PVOP_CALL0(unsigned long, pv_cpu_ops.read_cr4);
}
-static inline unsigned long __read_cr4_safe(void)
-{
- return PVOP_CALL0(unsigned long, pv_cpu_ops.read_cr4_safe);
-}
static inline void __write_cr4(unsigned long x)
{
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 7fa9e7740ba3..fcf243f077ac 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -108,7 +108,6 @@ struct pv_cpu_ops {
unsigned long (*read_cr0)(void);
void (*write_cr0)(unsigned long);
- unsigned long (*read_cr4_safe)(void);
unsigned long (*read_cr4)(void);
void (*write_cr4)(unsigned long);
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 587d7914ea4b..19a2224f9e16 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -59,22 +59,19 @@ static inline void native_write_cr3(unsigned long val)
static inline unsigned long native_read_cr4(void)
{
unsigned long val;
- asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" (__force_order));
- return val;
-}
-
-static inline unsigned long native_read_cr4_safe(void)
-{
- unsigned long val;
- /* This could fault if %cr4 does not exist. In x86_64, a cr4 always
- * exists, so it will never fail. */
#ifdef CONFIG_X86_32
+ /*
+ * This could fault if CR4 does not exist. Non-existent CR4
+ * is functionally equivalent to CR4 == 0. Keep it simple and pretend
+ * that CR4 == 0 on CPUs that don't have CR4.
+ */
asm volatile("1: mov %%cr4, %0\n"
"2:\n"
_ASM_EXTABLE(1b, 2b)
: "=r" (val), "=m" (__force_order) : "0" (0));
#else
- val = native_read_cr4();
+ /* CR4 always exists on x86_64. */
+ asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" (__force_order));
#endif
return val;
}
@@ -182,11 +179,6 @@ static inline unsigned long __read_cr4(void)
return native_read_cr4();
}
-static inline unsigned long __read_cr4_safe(void)
-{
- return native_read_cr4_safe();
-}
-
static inline void __write_cr4(unsigned long x)
{
native_write_cr4(x);
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index dee8a70382ba..6fa85944af83 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -81,7 +81,7 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
/* Initialize cr4 shadow for this CPU. */
static inline void cr4_init_shadow(void)
{
- this_cpu_write(cpu_tlbstate.cr4, __read_cr4_safe());
+ this_cpu_write(cpu_tlbstate.cr4, __read_cr4());
}
/* Set in this cpu's CR4. */
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 1acfd76e3e26..ed03b1c5b1b9 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -332,7 +332,6 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
.read_cr0 = native_read_cr0,
.write_cr0 = native_write_cr0,
.read_cr4 = native_read_cr4,
- .read_cr4_safe = native_read_cr4_safe,
.write_cr4 = native_write_cr4,
#ifdef CONFIG_X86_64
.read_cr8 = native_read_cr8,
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index d86be29c38c7..e5da9ba220d1 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -101,7 +101,7 @@ void __show_regs(struct pt_regs *regs, int all)
cr0 = read_cr0();
cr2 = read_cr2();
cr3 = read_cr3();
- cr4 = __read_cr4_safe();
+ cr4 = __read_cr4();
printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
cr0, cr2, cr3, cr4);
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 5930a4d191b4..09d245e8e2da 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1140,9 +1140,10 @@ void __init setup_arch(char **cmdline_p)
if (boot_cpu_data.cpuid_level >= 0) {
/*
* CPUs without CPUID don't have CR4. CPUs with CPUID
- * usually have CR4.
+ * usually have CR4. On CPUID-less CPUs, this avoids
+ * an unnecessary fixup, mainly for historical reasons.
*/
- mmu_cr4_features = __read_cr4_safe();
+ mmu_cr4_features = __read_cr4();
}
memblock_set_current_limit(get_max_mapped());
diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index b12c26e2e309..53cace2ec0e2 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -130,7 +130,7 @@ static void __save_processor_state(struct saved_context *ctxt)
ctxt->cr0 = read_cr0();
ctxt->cr2 = read_cr2();
ctxt->cr3 = read_cr3();
- ctxt->cr4 = __read_cr4_safe();
+ ctxt->cr4 = __read_cr4();
#ifdef CONFIG_X86_64
ctxt->cr8 = read_cr8();
#endif
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index b86ebb1a9a7f..e2cf8fcea6bb 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1237,7 +1237,6 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
.write_cr0 = xen_write_cr0,
.read_cr4 = native_read_cr4,
- .read_cr4_safe = native_read_cr4_safe,
.write_cr4 = xen_write_cr4,
#ifdef CONFIG_X86_64
--
2.7.4
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines
2016-09-28 19:34 ` [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines Andy Lutomirski
@ 2016-09-29 11:44 ` Borislav Petkov
2016-09-29 18:21 ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
1 sibling, 0 replies; 8+ messages in thread
From: Borislav Petkov @ 2016-09-29 11:44 UTC (permalink / raw)
To: Andy Lutomirski; +Cc: x86, david, Brian Gerst, linux-kernel, stable
On Wed, Sep 28, 2016 at 12:34:14PM -0700, Andy Lutomirski wrote:
> cr4_init_shadow() will panic on 486-like machines without CR4. Fix
> it using __read_cr4_safe().
>
> Cc: stable@vger.kernel.org
> Reported-by: david@saggiorato.net
> Fixes: 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/include/asm/tlbflush.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 6fa85944af83..dee8a70382ba 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -81,7 +81,7 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
> /* Initialize cr4 shadow for this CPU. */
> static inline void cr4_init_shadow(void)
> {
> - this_cpu_write(cpu_tlbstate.cr4, __read_cr4());
> + this_cpu_write(cpu_tlbstate.cr4, __read_cr4_safe());
> }
>
> /* Set in this cpu's CR4. */
> --
Reviewed-by: Borislav Petkov <bp@suse.de>
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486
2016-09-28 19:34 ` [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486 Andy Lutomirski
@ 2016-09-29 11:48 ` Borislav Petkov
2016-09-29 19:09 ` Andy Lutomirski
0 siblings, 1 reply; 8+ messages in thread
From: Borislav Petkov @ 2016-09-29 11:48 UTC (permalink / raw)
To: Andy Lutomirski; +Cc: x86, david, Brian Gerst, linux-kernel
On Wed, Sep 28, 2016 at 12:34:15PM -0700, Andy Lutomirski wrote:
> The condition for reading CR4 was wrong: there are some CPUs with
> CPUID but not CR4. Rather than trying to make the condition exact,
> using __read_cr4_safe().
>
> Reported-by: david@saggiorato.net
> Fixes: 18bc7bd523e0 ("x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features directly")
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/kernel/setup.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 0fa60f5f5a16..5930a4d191b4 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1137,9 +1137,13 @@ void __init setup_arch(char **cmdline_p)
> * auditing all the early-boot CR4 manipulation would be needed to
> * rule it out.
> */
> - if (boot_cpu_data.cpuid_level >= 0)
> - /* A CPU has %cr4 if and only if it has CPUID. */
> - mmu_cr4_features = __read_cr4();
> + if (boot_cpu_data.cpuid_level >= 0) {
> + /*
> + * CPUs without CPUID don't have CR4. CPUs with CPUID
> + * usually have CR4.
> + */
> + mmu_cr4_features = __read_cr4_safe();
> + }
Why are we even doing the CPUID check instead of unconditionally doing
__read_cr4_safe()?
The safe variant will give 0 on !CR4 machines.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
^ permalink raw reply [flat|nested] 8+ messages in thread
* [tip:x86/urgent] x86/init: Fix cr4_init_shadow() on CR4-less machines
2016-09-28 19:34 ` [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines Andy Lutomirski
2016-09-29 11:44 ` Borislav Petkov
@ 2016-09-29 18:21 ` tip-bot for Andy Lutomirski
1 sibling, 0 replies; 8+ messages in thread
From: tip-bot for Andy Lutomirski @ 2016-09-29 18:21 UTC (permalink / raw)
To: linux-tip-commits
Cc: linux-kernel, jpoimboe, peterz, tglx, torvalds, bp, dvlasenk,
brgerst, hpa, bp, mingo, luto
Commit-ID: e1bfc11c5a6f40222a698a818dc269113245820e
Gitweb: http://git.kernel.org/tip/e1bfc11c5a6f40222a698a818dc269113245820e
Author: Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 28 Sep 2016 12:34:14 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 29 Sep 2016 19:08:30 +0200
x86/init: Fix cr4_init_shadow() on CR4-less machines
cr4_init_shadow() will panic on 486-like machines without CR4. Fix
it using __read_cr4_safe().
Reported-by: david@saggiorato.net
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
Link: http://lkml.kernel.org/r/43a20f81fb504013bf613913dc25574b45336a61.1475091074.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/tlbflush.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 6fa8594..dee8a70 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -81,7 +81,7 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate);
/* Initialize cr4 shadow for this CPU. */
static inline void cr4_init_shadow(void)
{
- this_cpu_write(cpu_tlbstate.cr4, __read_cr4());
+ this_cpu_write(cpu_tlbstate.cr4, __read_cr4_safe());
}
/* Set in this cpu's CR4. */
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486
2016-09-29 11:48 ` Borislav Petkov
@ 2016-09-29 19:09 ` Andy Lutomirski
0 siblings, 0 replies; 8+ messages in thread
From: Andy Lutomirski @ 2016-09-29 19:09 UTC (permalink / raw)
To: Borislav Petkov; +Cc: Andy Lutomirski, X86 ML, david, Brian Gerst, linux-kernel
On Thu, Sep 29, 2016 at 4:48 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Wed, Sep 28, 2016 at 12:34:15PM -0700, Andy Lutomirski wrote:
>> The condition for reading CR4 was wrong: there are some CPUs with
>> CPUID but not CR4. Rather than trying to make the condition exact,
>> using __read_cr4_safe().
>>
>> Reported-by: david@saggiorato.net
>> Fixes: 18bc7bd523e0 ("x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features directly")
>> Signed-off-by: Andy Lutomirski <luto@kernel.org>
>> ---
>> arch/x86/kernel/setup.c | 10 +++++++---
>> 1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
>> index 0fa60f5f5a16..5930a4d191b4 100644
>> --- a/arch/x86/kernel/setup.c
>> +++ b/arch/x86/kernel/setup.c
>> @@ -1137,9 +1137,13 @@ void __init setup_arch(char **cmdline_p)
>> * auditing all the early-boot CR4 manipulation would be needed to
>> * rule it out.
>> */
>> - if (boot_cpu_data.cpuid_level >= 0)
>> - /* A CPU has %cr4 if and only if it has CPUID. */
>> - mmu_cr4_features = __read_cr4();
>> + if (boot_cpu_data.cpuid_level >= 0) {
>> + /*
>> + * CPUs without CPUID don't have CR4. CPUs with CPUID
>> + * usually have CR4.
>> + */
>> + mmu_cr4_features = __read_cr4_safe();
>> + }
>
> Why are we even doing the CPUID check instead of unconditionally doing
> __read_cr4_safe()?
>
> The safe variant will give 0 on !CR4 machines.
Will do.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2016-09-29 19:09 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-09-28 19:34 [PATCH 0/3] CR4 fixes (some are urgent) Andy Lutomirski
2016-09-28 19:34 ` [PATCH 1/3] x86/init: Fix cr4_init_shadow() on CR4-less machines Andy Lutomirski
2016-09-29 11:44 ` Borislav Petkov
2016-09-29 18:21 ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
2016-09-28 19:34 ` [PATCH 2/3] x86/boot: Fix another __read_cr4() case on 486 Andy Lutomirski
2016-09-29 11:48 ` Borislav Petkov
2016-09-29 19:09 ` Andy Lutomirski
2016-09-28 19:34 ` [PATCH 3/3] x86/asm: Get rid of __read_cr4_safe() Andy Lutomirski
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).