The following commit has been merged into the x86/core branch of tip:

Commit-ID: f9c9987bf52f4e42e940ae217333ebb5a4c3b506 Gitweb: https://git.kernel.org/tip/f9c9987bf52f4e42e940ae217333ebb5a4c3b506 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Thu, 15 Jun 2023 22:33:55 +02:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Tue, 20 Jun 2023 14:51:47 +02:00

x86/smp: Use dedicated cache-line for mwait_play_dead()

Monitoring idletask::thread_info::flags in mwait_play_dead() has been an obvious choice as all what is needed is a cache line which is not written by other CPUs.

But there is a use case where a "dead" CPU needs to be brought out of MWAIT: kexec().

This is required as kexec() can overwrite text, pagetables, stacks and the monitored cacheline of the original kernel. The latter causes MWAIT to resume execution which obviously causes havoc on the kexec kernel which results usually in triple faults.

Use a dedicated per CPU storage to prepare for that.

Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Ashok Raj ashok.raj@intel.com Reviewed-by: Borislav Petkov (AMD) bp@alien8.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230615193330.434553750@linutronix.de

--- arch/x86/kernel/smpboot.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 352f0ce..c5ac5d7 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -101,6 +101,17 @@ EXPORT_PER_CPU_SYMBOL(cpu_die_map); DEFINE_PER_CPU_READ_MOSTLY(struct cpuinfo_x86, cpu_info); EXPORT_PER_CPU_SYMBOL(cpu_info);

+struct mwait_cpu_dead { + unsigned int control; + unsigned int status; +}; + +/* + * Cache line aligned data for mwait_play_dead(). Separate on purpose so + * that it's unlikely to be touched by other CPUs. + */ +static DEFINE_PER_CPU_ALIGNED(struct mwait_cpu_dead, mwait_cpu_dead); + /* Logical package management. We might want to allocate that dynamically */ unsigned int __max_logical_packages __read_mostly; EXPORT_SYMBOL(__max_logical_packages); @@ -1758,10 +1769,10 @@ EXPORT_SYMBOL_GPL(cond_wakeup_cpu0); */ static inline void mwait_play_dead(void) { + struct mwait_cpu_dead *md = this_cpu_ptr(&mwait_cpu_dead); unsigned int eax, ebx, ecx, edx; unsigned int highest_cstate = 0; unsigned int highest_subcstate = 0; - void *mwait_ptr; int i;

if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || @@ -1796,13 +1807,6 @@ static inline void mwait_play_dead(void) (highest_subcstate - 1); }

- /* - * This should be a memory location in a cache line which is - * unlikely to be touched by other processors. The actual - * content is immaterial as it is not actually modified in any way. - */ - mwait_ptr = &current_thread_info()->flags; - wbinvd();

while (1) { @@ -1814,9 +1818,9 @@ static inline void mwait_play_dead(void) * case where we return around the loop. */ mb(); - clflush(mwait_ptr); + clflush(md); mb(); - __monitor(mwait_ptr, 0, 0); + __monitor(md, 0, 0); mb(); __mwait(eax, 0);