diff mbox series

[v6,07/18] arm64: KVM/mm: Move SEA handling behind a single 'claim' interface

Message ID 20180921221705.6478-8-james.morse@arm.com (mailing list archive)
State Changes Requested, archived
Headers show
Series APEI in_nmi() rework | expand

Commit Message

James Morse Sept. 21, 2018, 10:16 p.m. UTC 
To split up APEIs in_nmi() path, we need the nmi-like callers to always
be in_nmi(). Add a helper to do the work and claim the notification.

When KVM or the arch code takes an exception that might be a RAS
notification, it asks the APEI firmware-first code whether it wants
to claim the exception. We can then go on to see if (a future)
kernel-first mechanism wants to claim the notification, before
falling through to the existing default behaviour.

The NOTIFY_SEA code was merged before we had multiple, possibly
interacting, NMI-like notifications and the need to consider kernel
first in the future. Make the 'claiming' behaviour explicit.

As we're restructuring the APEI code to allow multiple NMI-like
notifications, any notification that might interrupt interrupts-masked
code must always be wrapped in nmi_enter()/nmi_exit(). This allows APEI
to use in_nmi() to use the right fixmap entries.

We mask SError over this window to prevent an asynchronous RAS error
arriving and tripping 'nmi_enter()'s BUG_ON(in_nmi()).

Signed-off-by: James Morse <james.morse@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>

---
Why does apei_claim_sea() take a pt_regs? This gets used later to take
APEI by the hand through NMI->IRQ context, depending on what we
interrupted.

Changes since v4:
 * Made irqs-unmasked comment a lockdep assert.

Changes since v3:
 * Removed spurious whitespace change
 * Updated comment in acpi.c to cover SError masking

Changes since v2:
 * Added dummy definition for !ACPI and culled IS_ENABLED() checks.

squash: make 'call with irqs unmaksed' a lockdep assert, much better
---
 arch/arm64/include/asm/acpi.h      |  4 ++++
 arch/arm64/include/asm/daifflags.h |  1 +
 arch/arm64/include/asm/kvm_ras.h   | 16 +++++++++++++++-
 arch/arm64/kernel/acpi.c           | 29 +++++++++++++++++++++++++++++
 arch/arm64/mm/fault.c              | 24 +++++-------------------
 5 files changed, 54 insertions(+), 20 deletions(-)

Comments

Borislav Petkov Oct. 12, 2018, 10:02 a.m. UTC | #1 
On Fri, Sep 21, 2018 at 11:16:54PM +0100, James Morse wrote:
> To split up APEIs in_nmi() path, we need the nmi-like callers to always
> be in_nmi(). Add a helper to do the work and claim the notification.
> 
> When KVM or the arch code takes an exception that might be a RAS
> notification, it asks the APEI firmware-first code whether it wants
> to claim the exception. We can then go on to see if (a future)
> kernel-first mechanism wants to claim the notification, before
> falling through to the existing default behaviour.
> 
> The NOTIFY_SEA code was merged before we had multiple, possibly
> interacting, NMI-like notifications and the need to consider kernel
> first in the future. Make the 'claiming' behaviour explicit.
> 
> As we're restructuring the APEI code to allow multiple NMI-like
> notifications, any notification that might interrupt interrupts-masked
> code must always be wrapped in nmi_enter()/nmi_exit(). This allows APEI
> to use in_nmi() to use the right fixmap entries.
> 
> We mask SError over this window to prevent an asynchronous RAS error
> arriving and tripping 'nmi_enter()'s BUG_ON(in_nmi()).
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> Tested-by: Tyler Baicar <tbaicar@codeaurora.org>

...

> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> index ed46dc188b22..a9b8bba014b5 100644
> --- a/arch/arm64/kernel/acpi.c
> +++ b/arch/arm64/kernel/acpi.c
> @@ -28,8 +28,10 @@
>  #include <linux/smp.h>
>  #include <linux/serial_core.h>
>  
> +#include <acpi/ghes.h>
>  #include <asm/cputype.h>
>  #include <asm/cpu_ops.h>
> +#include <asm/daifflags.h>
>  #include <asm/pgtable.h>
>  #include <asm/smp_plat.h>
>  
> @@ -257,3 +259,30 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
>  		return __pgprot(PROT_NORMAL_NC);
>  	return __pgprot(PROT_DEVICE_nGnRnE);
>  }
> +
> +/*
> + * Claim Synchronous External Aborts as a firmware first notification.
> + *
> + * Used by KVM and the arch do_sea handler.
> + * @regs may be NULL when called from process context.
> + */
> +int apei_claim_sea(struct pt_regs *regs)
> +{
> +	int err = -ENOENT;
> +	unsigned long current_flags = arch_local_save_flags();
> +
> +	if (!IS_ENABLED(CONFIG_ACPI_APEI_SEA))
> +		return err;

I don't know what side effects arch_local_save_flags() has on ARM but if
we return here, it looks to me like useless work.
James Morse Oct. 12, 2018, 5:18 p.m. UTC | #2 
Hi Boris,

On 12/10/2018 11:02, Borislav Petkov wrote:
> On Fri, Sep 21, 2018 at 11:16:54PM +0100, James Morse wrote:
>> To split up APEIs in_nmi() path, we need the nmi-like callers to always
>> be in_nmi(). Add a helper to do the work and claim the notification.
>>
>> When KVM or the arch code takes an exception that might be a RAS
>> notification, it asks the APEI firmware-first code whether it wants
>> to claim the exception. We can then go on to see if (a future)
>> kernel-first mechanism wants to claim the notification, before
>> falling through to the existing default behaviour.
>>
>> The NOTIFY_SEA code was merged before we had multiple, possibly
>> interacting, NMI-like notifications and the need to consider kernel
>> first in the future. Make the 'claiming' behaviour explicit.
>>
>> As we're restructuring the APEI code to allow multiple NMI-like
>> notifications, any notification that might interrupt interrupts-masked
>> code must always be wrapped in nmi_enter()/nmi_exit(). This allows APEI
>> to use in_nmi() to use the right fixmap entries.
>>
>> We mask SError over this window to prevent an asynchronous RAS error
>> arriving and tripping 'nmi_enter()'s BUG_ON(in_nmi()).

>> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
>> index ed46dc188b22..a9b8bba014b5 100644
>> --- a/arch/arm64/kernel/acpi.c
>> +++ b/arch/arm64/kernel/acpi.c
>> @@ -257,3 +259,30 @@ pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
>>  		return __pgprot(PROT_NORMAL_NC);
>>  	return __pgprot(PROT_DEVICE_nGnRnE);
>>  }
>> +
>> +/*
>> + * Claim Synchronous External Aborts as a firmware first notification.
>> + *
>> + * Used by KVM and the arch do_sea handler.
>> + * @regs may be NULL when called from process context.
>> + */
>> +int apei_claim_sea(struct pt_regs *regs)
>> +{
>> +	int err = -ENOENT;
>> +	unsigned long current_flags = arch_local_save_flags();
>> +
>> +	if (!IS_ENABLED(CONFIG_ACPI_APEI_SEA))
>> +		return err;
> 
> I don't know what side effects arch_local_save_flags() has on ARM but if

It reads the current 'masked' state for IRQs, debug exceptions and 'SError'.


> we return here, it looks to me like useless work.

Yes. I lazily assume the compiler will rip that out as the value is never used.
But in this case it can't, because its wrapped in asm-volatile, so it doesn't
know it has no side-effects.

I'll move it further down.

Thanks!

James
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
index 709208dfdc8b..f722d2d6bf2b 100644
--- a/arch/arm64/include/asm/acpi.h
+++ b/arch/arm64/include/asm/acpi.h
@@ -18,6 +18,7 @@ 
 
 #include <asm/cputype.h>
 #include <asm/io.h>
+#include <asm/ptrace.h>
 #include <asm/smp_plat.h>
 #include <asm/tlbflush.h>
 
@@ -139,6 +140,9 @@  static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
 {
 	return __acpi_get_mem_attribute(addr);
 }
+int apei_claim_sea(struct pt_regs *regs);
+#else
+static inline int apei_claim_sea(struct pt_regs *regs) { return -ENOENT; }
 #endif /* CONFIG_ACPI_APEI */
 
 #ifdef CONFIG_ACPI_NUMA
diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index 22e4c83de5a5..cbd753855bf3 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -20,6 +20,7 @@ 
 
 #define DAIF_PROCCTX		0
 #define DAIF_PROCCTX_NOIRQ	PSR_I_BIT
+#define DAIF_ERRCTX		(PSR_I_BIT | PSR_A_BIT)
 
 /* mask/save/unmask/restore all exceptions, including interrupts. */
 static inline void local_daif_mask(void)
diff --git a/arch/arm64/include/asm/kvm_ras.h b/arch/arm64/include/asm/kvm_ras.h
index 5f72b07b7912..5b56e7e297b1 100644
--- a/arch/arm64/include/asm/kvm_ras.h
+++ b/arch/arm64/include/asm/kvm_ras.h
@@ -4,8 +4,22 @@ 
 #ifndef __ARM64_KVM_RAS_H__
 #define __ARM64_KVM_RAS_H__
 
+#include <linux/acpi.h>
+#include <linux/errno.h>
 #include <linux/types.h>
 
-int kvm_handle_guest_sea(phys_addr_t addr, unsigned int esr);
+#include <asm/acpi.h>
+
+/*
+ * Was this synchronous external abort a RAS notification?
+ * Returns '0' for errors handled by some RAS subsystem, or -ENOENT.
+ */
+static inline int kvm_handle_guest_sea(phys_addr_t addr, unsigned int esr)
+{
+	/* apei_claim_sea(NULL) expects to mask interrupts itself */
+	lockdep_assert_irqs_enabled();
+
+	return apei_claim_sea(NULL);
+}
 
 #endif /* __ARM64_KVM_RAS_H__ */
diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index ed46dc188b22..a9b8bba014b5 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -28,8 +28,10 @@ 
 #include <linux/smp.h>
 #include <linux/serial_core.h>
 
+#include <acpi/ghes.h>
 #include <asm/cputype.h>
 #include <asm/cpu_ops.h>
+#include <asm/daifflags.h>
 #include <asm/pgtable.h>
 #include <asm/smp_plat.h>
 
@@ -257,3 +259,30 @@  pgprot_t __acpi_get_mem_attribute(phys_addr_t addr)
 		return __pgprot(PROT_NORMAL_NC);
 	return __pgprot(PROT_DEVICE_nGnRnE);
 }
+
+/*
+ * Claim Synchronous External Aborts as a firmware first notification.
+ *
+ * Used by KVM and the arch do_sea handler.
+ * @regs may be NULL when called from process context.
+ */
+int apei_claim_sea(struct pt_regs *regs)
+{
+	int err = -ENOENT;
+	unsigned long current_flags = arch_local_save_flags();
+
+	if (!IS_ENABLED(CONFIG_ACPI_APEI_SEA))
+		return err;
+
+	/*
+	 * SEA can interrupt SError, mask it and describe this as an NMI so
+	 * that APEI defers the handling.
+	 */
+	local_daif_restore(DAIF_ERRCTX);
+	nmi_enter();
+	err = ghes_notify_sea();
+	nmi_exit();
+	local_daif_restore(current_flags);
+
+	return err;
+}
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 1a30d7a8c9bf..2c38776bb71f 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -18,6 +18,7 @@ 
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <linux/acpi.h>
 #include <linux/extable.h>
 #include <linux/signal.h>
 #include <linux/mm.h>
@@ -33,6 +34,7 @@ 
 #include <linux/preempt.h>
 #include <linux/hugetlb.h>
 
+#include <asm/acpi.h>
 #include <asm/bug.h>
 #include <asm/cmpxchg.h>
 #include <asm/cpufeature.h>
@@ -45,8 +47,6 @@ 
 #include <asm/tlbflush.h>
 #include <asm/traps.h>
 
-#include <acpi/ghes.h>
-
 struct fault_info {
 	int	(*fn)(unsigned long addr, unsigned int esr,
 		      struct pt_regs *regs);
@@ -631,19 +631,10 @@  static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 	inf = esr_to_fault_info(esr);
 
 	/*
-	 * Synchronous aborts may interrupt code which had interrupts masked.
-	 * Before calling out into the wider kernel tell the interested
-	 * subsystems.
+	 * Return value ignored as we rely on signal merging.
+	 * Future patches will make this more robust.
 	 */
-	if (IS_ENABLED(CONFIG_ACPI_APEI_SEA)) {
-		if (interrupts_enabled(regs))
-			nmi_enter();
-
-		ghes_notify_sea();
-
-		if (interrupts_enabled(regs))
-			nmi_exit();
-	}
+	apei_claim_sea(regs);
 
 	clear_siginfo(&info);
 	info.si_signo = inf->sig;
@@ -725,11 +716,6 @@  static const struct fault_info fault_info[] = {
 	{ do_bad,		SIGKILL, SI_KERNEL,	"unknown 63"			},
 };
 
-int kvm_handle_guest_sea(phys_addr_t addr, unsigned int esr)
-{
-	return ghes_notify_sea();
-}
-
 asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
 					 struct pt_regs *regs)
 {