Messages in this thread | | | Date | Tue, 24 Oct 2023 19:01:42 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/2] x86: Enable x2apic during resume from suspend if used previously |
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* Mario Limonciello <mario.limonciello@amd.com> wrote:
> +Tom > > On 10/24/2023 03:36, Ingo Molnar wrote: > > > > * Mario Limonciello <mario.limonciello@amd.com> 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@vger.kernel.org # 6.5+ > > > Fixes: 0c7ffa32dbd6 ("x86/smpboot/64: Implement arch_cpuhp_init_parallel_bringup() and enable it") > > > Signed-off-by: Mario Limonciello <mario.limonciello@amd.com> > > > --- > > > 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
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