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Message-ID: <6894bebf-15ed-4bd2-aebc-f4ac0a30a395@amd.com>
Date: Tue, 24 Oct 2023 10:36:18 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Ingo Molnar <mingo@...nel.org>,
Tom Lendacky <thomas.lendacky@....com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Borislav Petkov <bp@...en8.de>,
Thomas Gleixner <tglx@...utronix.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Sandipan Das <sandipan.das@....com>,
"H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
x86@...nel.org, linux-pm@...r.kernel.org, rafael@...nel.org,
pavel@....cz, linux-perf-users@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 1/2] x86: Enable x2apic during resume from suspend if used
previously
+Tom
On 10/24/2023 03:36, Ingo Molnar wrote:
>
> * Mario Limonciello <mario.limonciello@....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@...r.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@....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.
I've looped Tom in to comment whether it's possible to improve AMD-SEV
as well.
>
> Also, side note #1: curly braces should be balanced.
>
>> #endif
>> initial_code = (unsigned long)wakeup_long64;
>> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
>> index ea6995920b7a..fcfa79105928 100644
>> --- a/arch/x86/kernel/head_64.S
>> +++ b/arch/x86/kernel/head_64.S
>> @@ -236,10 +236,15 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
>> * used to look up the CPU number. For booting a single CPU, the
>> * CPU number is encoded in smpboot_control.
>> *
>> + * Bit 30 STARTUP_ENABLE_X2APIC (Enable X2APIC mode)
>> * Bit 31 STARTUP_READ_APICID (Read APICID from APIC)
>> * Bit 0-23 CPU# if STARTUP_xx flags are not set
>
> Side note #2: you mixed up the comment ordering here.
>
> Thanks,
>
> Ingo
Sure, thanks for the feedback. I'll adjust the style for v2.
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