Re: [PATCHv2 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

[Huang, Kai]

> > +	.text
> > +	.align PAGE_SIZE
> > +SYM_FUNC_START(asm_acpi_mp_play_dead)
> > +	/* Load address of reset vector into RCX to jump when kernel is ready */
> > +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> > +
> > +	/* Turn off global entries. Following CR3 write will flush them. */
> > +	movq	%cr4, %rdx
> > +	andq	$~(X86_CR4_PGE), %rdx
> > +	movq	%rdx, %cr4
> > +
> > +	/* Switch to identity mapping */
> > +	movq	acpi_mp_pgd(%rip), %rax
> > +	movq	%rax, %cr3
> 
> Do we need to switch back to kernel direct-map page table after CPU is wake up
> again?  We do support normal CPU offline/online, but not limited to kexec,
> right?

Please ignore this.  I found if I am reading right even for TDX guest the new
online cpu will start with trampoline_start64 assembly, so it will load kernel
page table anyway.  Sorry for the noise.

[...]


> > +	for (int i = 0; i < nr_pfn_mapped; i++) {
> > +		unsigned long mstart, mend;
> > +		mstart = pfn_mapped[i].start << PAGE_SHIFT;
> > +		mend   = pfn_mapped[i].end << PAGE_SHIFT;
> > +		if (kernel_ident_mapping_init(&info, pgd, mstart, mend))
> > +			return -ENOMEM;
> > +	}
> 
> This is for kexec() IIUC.  Add a comment?
> 
> If we consider normal CPU offline/online case, then I don't think we need the
> identity mapping for all memory?
> 

Also this one. :-)

>