On 4/12/2023 10:59 PM, Michael Kelley (LINUX) wrote:
#ifdef CONFIG_AMD_MEM_ENCRYPT
#define GHCB_USAGE_HYPERV_CALL 1
+static u8 ap_start_input_arg[PAGE_SIZE] __bss_decrypted __aligned(PAGE_SIZE);
+static u8 ap_start_stack[PAGE_SIZE] __aligned(PAGE_SIZE);
Just a question: ap_start_stack is a static variable that gets used as the
starting stack for every AP. So obviously, once each AP is started, we must
be sure that the AP moves off the ap_start_stack before the next AP is
started. How is that synchronization done? I see that do_boot_cpu() is
where the wakeup_secondary_cpu() function is called. Then there's
some waiting until the AP completes "initial initialization" per the
comment in the code. Is there where we know that the AP is no
longer using ap_start_stack?
Hi Micahel:
secondary_startup_64_no_verify() in the head_64.S initializes
a boot time stack to replace the old stack. It's very begining stage of
starting AP. The initial_stack was initialized with idle->thread.sp in
the do_boot_cpu(). The AP is started one by one in current code and so
It's safe to reuse the stack for all APs to boot up.
278 /*
279 * Setup a boot time stack - Any secondary CPU will have lost
its stack
280 * by now because the cr3-switch above unmaps the real-mode stack
281 */
282 movq initial_stack(%rip), %rsp
283
