* Mario Limonciello <mario.limonciello@xxxxxxx> wrote:
+Tom
On 10/24/2023 03:36, Ingo Molnar wrote:
* Mario Limonciello <mario.limonciello@xxxxxxx> wrote:
If x2apic was enabled during boot with parallel startup
it will be needed during resume from suspend to ram as well.
Store whether to enable into the smpboot_control global variable
and during startup re-enable it if necessary.
Cc: stable@xxxxxxxxxxxxxxx # 6.5+
Fixes: 0c7ffa32dbd6 ("x86/smpboot/64: Implement arch_cpuhp_init_parallel_bringup() and enable it")
Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
---
arch/x86/include/asm/smp.h | 1 +
arch/x86/kernel/acpi/sleep.c | 12 ++++++++----
arch/x86/kernel/head_64.S | 15 +++++++++++++++
3 files changed, 24 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index c31c633419fe..86584ffaebc3 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -190,6 +190,7 @@ extern unsigned long apic_mmio_base;
#endif /* !__ASSEMBLY__ */
/* Control bits for startup_64 */
+#define STARTUP_ENABLE_X2APIC 0x40000000
#define STARTUP_READ_APICID 0x80000000
/* Top 8 bits are reserved for control */
diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 6dfecb27b846..29734a1299f6 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -11,6 +11,7 @@
#include <linux/dmi.h>
#include <linux/cpumask.h>
#include <linux/pgtable.h>
+#include <asm/apic.h>
#include <asm/segment.h>
#include <asm/desc.h>
#include <asm/cacheflush.h>
@@ -129,11 +130,14 @@ int x86_acpi_suspend_lowlevel(void)
*/
current->thread.sp = (unsigned long)temp_stack + sizeof(temp_stack);
/*
- * Ensure the CPU knows which one it is when it comes back, if
- * it isn't in parallel mode and expected to work that out for
- * itself.
+ * Ensure x2apic is re-enabled if necessary and the CPU knows which
+ * one it is when it comes back, if it isn't in parallel mode and
+ * expected to work that out for itself.
*/
- if (!(smpboot_control & STARTUP_PARALLEL_MASK))
+ if (smpboot_control & STARTUP_PARALLEL_MASK) {
+ if (x2apic_enabled())
+ smpboot_control |= STARTUP_ENABLE_X2APIC;
+ } else
smpboot_control = smp_processor_id();
Yeah, so instead of adding further kludges to the 'parallel bringup is
possible' code path, which is arguably a functional feature that shouldn't
have hardware-management coupled to it, would it be possible to fix
parallel bringup to AMD-SEV systems, so that this code path isn't a
quirk-dependent "parallel boot" codepath, but simply the "x86 SMP boot
codepath", where all SMP x86 systems do a parallel bootup?
The original commit by Thomas says:
0c7ffa32dbd6 ("x86/smpboot/64: Implement arch_cpuhp_init_parallel_bringup() and enable it")
| Unfortunately there is no RDMSR GHCB protocol at the moment, so enabling
| AMD-SEV guests for parallel startup needs some more thought.
But that was half a year ago, isn't there RDMSR GHCB access code available now?
This code would all read a lot more natural if it was the regular x86 SMP
bootup path - which it is 'almost' today already, modulo quirk.
Obviously coupling functional features with hardware quirks is fragile, for
example your patch extending x86 SMP parallel bringup doesn't extend the
AMD-SEV case, which may or may not matter in practice.
So, if it's possible, it would be nice to fix AMD-SEV systems as well and
remove this artificial coupling.
It probably isn't clear since I didn't mention it in the commit message, but
this is not a system that supports AMD-SEV. This is a workstation that
supports x2apic. I'll clarify that for V2.
Yes, I suspected as much, but that's irrelevant to the arguments I
outlined, that extending upon this quirk that makes SMP parallel bringup HW
environment dependent, and then coupling s2ram x2apic re-enablement to that
functional feature is inviting trouble in the long run.
For example, what guarantees that the x2apic will be turned back on after
suspend if a system is booted with maxcpus=1?
Obviously something very close to your fix is needed.
I've looped Tom in to comment whether it's possible to improve AMD-SEV as
well.
Thanks!
Ingo