On Tue, May 28, 2024 at 12:55:21PM +0300, Kirill A. Shutemov wrote:

MADT Multiprocessor Wakeup structure version 1 brings support of CPU

s/of /for /

offlining: BIOS provides a reset vector where the CPU has to jump to
for offlining itself. The new TEST mailbox command can be used to test
whether the CPU offlined itself which means the BIOS has control over
the CPU and can online it again via the ACPI MADT wakeup method.

Add CPU offling support for the ACPI MADT wakeup method by implementing

Unknown word [offling] in commit message.

Please introduce a spellchecker into your patch creation workflow.

custom cpu_die(), play_dead() and stop_this_cpu() SMP operations.

CPU offlining makes is possible to hand over secondary CPUs over kexec,

s/is /it /

not limiting the second kernel to a single CPU.

...

+/*
+ * Make sure asm_acpi_mp_play_dead() is present in the identity mapping at
+ * the same place as in the kernel page tables. asm_acpi_mp_play_dead() switches
+ * to the identity mapping and the function has be present at the same spot in
+ * the virtual address space before and after switching page tables.
+ */
+static int __init init_transition_pgtable(pgd_t *pgd)

This looks like a generic helper which should be in set_memory.c. And
looking at that file, there's populate_pgd() which does pretty much the
same thing, if I squint real hard.

Let's tone down the duplication.

+{
+	pgprot_t prot = PAGE_KERNEL_EXEC_NOENC;
+	unsigned long vaddr, paddr;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	vaddr = (unsigned long)asm_acpi_mp_play_dead;
+	pgd += pgd_index(vaddr);
+	if (!pgd_present(*pgd)) {
+		p4d = (p4d_t *)alloc_pgt_page(NULL);
+		if (!p4d)
+			return -ENOMEM;
+		set_pgd(pgd, __pgd(__pa(p4d) | _KERNPG_TABLE));
+	}
+	p4d = p4d_offset(pgd, vaddr);
+	if (!p4d_present(*p4d)) {
+		pud = (pud_t *)alloc_pgt_page(NULL);
+		if (!pud)
+			return -ENOMEM;
+		set_p4d(p4d, __p4d(__pa(pud) | _KERNPG_TABLE));
+	}
+	pud = pud_offset(p4d, vaddr);
+	if (!pud_present(*pud)) {
+		pmd = (pmd_t *)alloc_pgt_page(NULL);
+		if (!pmd)
+			return -ENOMEM;
+		set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
+	}
+	pmd = pmd_offset(pud, vaddr);
+	if (!pmd_present(*pmd)) {
+		pte = (pte_t *)alloc_pgt_page(NULL);
+		if (!pte)
+			return -ENOMEM;
+		set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
+	}
+	pte = pte_offset_kernel(pmd, vaddr);
+
+	paddr = __pa(vaddr);
+	set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, prot));
+
+	return 0;
+}

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette