On 27/08/2019 05:52, Chao Gao wrote:
> On Mon, Aug 26, 2019 at 04:07:59PM +0800, Chao Gao wrote:
>> On Fri, Aug 23, 2019 at 09:46:37AM +0100, Sergey Dyasli wrote:
>>> On 19/08/2019 02:25, Chao Gao wrote:
>>>> register an nmi callback. And this callback does busy-loop on threads
>>>> which are waiting for loading completion. Control threads send NMI to
>>>> slave threads to prevent NMI acceptance during ucode loading.
>>>>
>>>> Signed-off-by: Chao Gao <chao....@intel.com>
>>>> ---
>>>> Changes in v9:
>>>> - control threads send NMI to all other threads. Slave threads will
>>>> stay in the NMI handling to prevent NMI acceptance during ucode
>>>> loading. Note that self-nmi is invalid according to SDM.
>>>
>>> To me this looks like a half-measure: why keep only slave threads in
>>> the NMI handler, when master threads can update the microcode from
>>> inside the NMI handler as well?
>>
>> No special reason. Because the issue we want to address is that slave
>> threads might go to handle NMI and access MSRs when master thread is
>> loading ucode. So we only keep slave threads in the NMI handler.
>>
>>>
>>> You mention that self-nmi is invalid, but Xen has self_nmi() which is
>>> used for apply_alternatives() during boot, so can be trusted to work.
>>
>> Sorry, I meant using self shorthand to send self-nmi. I tried to use
>> self shorthand but got APIC error. And I agree that it is better to
>> make slave thread call self_nmi() itself.
>>
>>>
>>> I experimented a bit with the following approach: after loading_state
>>> becomes LOADING_CALLIN, each cpu issues a self_nmi() and rendezvous
>>> via cpu_callin_map into LOADING_ENTER to do a ucode update directly in
>>> the NMI handler. And it seems to work.
>>>
>>> Separate question is about the safety of this approach: can we be sure
>>> that a ucode update would not reset the status of the NMI latch? I.e.
>>> can it cause another NMI to be delivered while Xen already handles one?
>>
>> Ashok, what's your opinion on Sergey's approach and his concern?
>
> Hi Sergey,
>
> I talked with Ashok. We think your approach is better. I will follow
> your approach in v10. It would be much helpful if you post your patch
> so that I can just rebase it onto other patches.
Sure thing. The below code is my first attempt at improving the original
patch. It can benefit from some further refactoring.
---
xen/arch/x86/microcode.c | 108 ++++++++++++++++++++++++++++-----------
1 file changed, 79 insertions(+), 29 deletions(-)
diff --git a/xen/arch/x86/microcode.c b/xen/arch/x86/microcode.c
index 91f9e811f8..ba2363406f 100644
--- a/xen/arch/x86/microcode.c
+++ b/xen/arch/x86/microcode.c
@@ -36,8 +36,10 @@
#include <xen/earlycpio.h>
#include <xen/watchdog.h>
+#include <asm/apic.h>
#include <asm/delay.h>
#include <asm/msr.h>
+#include <asm/nmi.h>
#include <asm/processor.h>
#include <asm/setup.h>
#include <asm/microcode.h>
@@ -232,6 +234,7 @@ DEFINE_PER_CPU(struct cpu_signature, cpu_sig);
*/
static cpumask_t cpu_callin_map;
static atomic_t cpu_out, cpu_updated;
+struct microcode_patch *nmi_patch;
/*
* Return a patch that covers current CPU. If there are multiple patches,
@@ -337,15 +340,25 @@ static int microcode_update_cpu(const struct
microcode_patch *patch)
return err;
}
+static void slave_thread_work(void)
+{
+ /* Do nothing, just wait */
+ while ( loading_state != LOADING_EXIT )
+ cpu_relax();
+}
+
static int slave_thread_fn(void)
{
- unsigned int cpu = smp_processor_id();
unsigned int master = cpumask_first(this_cpu(cpu_sibling_mask));
while ( loading_state != LOADING_CALLIN )
+ {
+ if ( loading_state == LOADING_EXIT )
+ return 0;
cpu_relax();
+ }
- cpumask_set_cpu(cpu, &cpu_callin_map);
+ self_nmi();
while ( loading_state != LOADING_EXIT )
cpu_relax();
@@ -356,30 +369,35 @@ static int slave_thread_fn(void)
return 0;
}
-static int master_thread_fn(const struct microcode_patch *patch)
+static void master_thread_work(void)
{
- unsigned int cpu = smp_processor_id();
- int ret = 0;
-
- while ( loading_state != LOADING_CALLIN )
- cpu_relax();
-
- cpumask_set_cpu(cpu, &cpu_callin_map);
+ int ret;
while ( loading_state != LOADING_ENTER )
+ {
+ if ( loading_state == LOADING_EXIT )
+ return;
cpu_relax();
+ }
- /*
- * If an error happened, control thread would set 'loading_state'
- * to LOADING_EXIT. Don't perform ucode loading for this case
- */
- if ( loading_state == LOADING_EXIT )
- return ret;
-
- ret = microcode_ops->apply_microcode(patch);
+ ret = microcode_ops->apply_microcode(nmi_patch);
if ( !ret )
atomic_inc(&cpu_updated);
atomic_inc(&cpu_out);
+}
+
+static int master_thread_fn(const struct microcode_patch *patch)
+{
+ int ret = 0;
+
+ while ( loading_state != LOADING_CALLIN )
+ {
+ if ( loading_state == LOADING_EXIT )
+ return ret;
+ cpu_relax();
+ }
+
+ self_nmi();
while ( loading_state != LOADING_EXIT )
cpu_relax();
@@ -387,35 +405,40 @@ static int master_thread_fn(const struct microcode_patch
*patch)
return ret;
}
-static int control_thread_fn(const struct microcode_patch *patch)
+static void control_thread_work(void)
{
- unsigned int cpu = smp_processor_id(), done;
- unsigned long tick;
int ret;
- /* Allow threads to call in */
- loading_state = LOADING_CALLIN;
- smp_mb();
-
- cpumask_set_cpu(cpu, &cpu_callin_map);
-
/* Waiting for all threads calling in */
ret = wait_for_condition(wait_cpu_callin,
(void *)(unsigned long)num_online_cpus(),
MICROCODE_CALLIN_TIMEOUT_US);
if ( ret ) {
loading_state = LOADING_EXIT;
- return ret;
+ return;
}
/* Let master threads load the given ucode update */
loading_state = LOADING_ENTER;
smp_mb();
- ret = microcode_ops->apply_microcode(patch);
+ ret = microcode_ops->apply_microcode(nmi_patch);
if ( !ret )
atomic_inc(&cpu_updated);
atomic_inc(&cpu_out);
+}
+
+static int control_thread_fn(const struct microcode_patch *patch)
+{
+ unsigned int done;
+ unsigned long tick;
+ int ret;
+
+ /* Allow threads to call in */
+ loading_state = LOADING_CALLIN;
+ smp_mb();
+
+ self_nmi();
tick = rdtsc_ordered();
/* Waiting for master threads finishing update */
@@ -481,12 +504,35 @@ static int do_microcode_update(void *patch)
return ret;
}
+static int microcode_nmi_callback(const struct cpu_user_regs *regs, int cpu)
+{
+ unsigned int master = cpumask_first(this_cpu(cpu_sibling_mask));
+ unsigned int controller = cpumask_first(&cpu_online_map);
+
+ /* System-generated NMI, will be ignored */
+ if ( loading_state == LOADING_PREPARE )
+ return 0;
+
+ ASSERT(loading_state == LOADING_CALLIN);
+ cpumask_set_cpu(cpu, &cpu_callin_map);
+
+ if ( cpu == controller )
+ control_thread_work();
+ else if ( cpu == master )
+ master_thread_work();
+ else
+ slave_thread_work();
+
+ return 0;
+}
+
int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
{
int ret;
void *buffer;
unsigned int cpu, updated;
struct microcode_patch *patch;
+ nmi_callback_t *saved_nmi_callback;
if ( len != (uint32_t)len )
return -E2BIG;
@@ -551,6 +597,9 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void)
buf, unsigned long len)
* watchdog timeout.
*/
watchdog_disable();
+
+ nmi_patch = patch;
+ saved_nmi_callback = set_nmi_callback(microcode_nmi_callback);
/*
* Late loading dance. Why the heavy-handed stop_machine effort?
*
@@ -563,6 +612,7 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void)
buf, unsigned long len)
* conservative and good.
*/
ret = stop_machine_run(do_microcode_update, patch, NR_CPUS);
+ set_nmi_callback(saved_nmi_callback);
watchdog_enable();
updated = atomic_read(&cpu_updated);
--
2.17.1
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