Commit 799de1ba authored by Joerg Roedel's avatar Joerg Roedel Committed by Borislav Petkov
Browse files

x86/sev-es: Optimize __sev_es_ist_enter() for better readability 



Reorganize the code and improve the comments to make the function more
readable and easier to understand.

Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210303141716.29223-4-joro@8bytes.org
parent f15a0a73

arch/x86/kernel/sev-es.c

+24 −12
Original line number Diff line number Diff line
@@ -137,29 +137,41 @@ static __always_inline bool on_vc_stack(struct pt_regs *regs) 
}



/*

 * This function handles the case when an NMI is raised in the #VC exception

 * handler entry code. In this case, the IST entry for #VC must be adjusted, so

 * that any subsequent #VC exception will not overwrite the stack contents of the

 * interrupted #VC handler.

 * This function handles the case when an NMI is raised in the #VC

 * exception handler entry code, before the #VC handler has switched off

 * its IST stack. In this case, the IST entry for #VC must be adjusted,

 * so that any nested #VC exception will not overwrite the stack

 * contents of the interrupted #VC handler.

 *

 * The IST entry is adjusted unconditionally so that it can be also be

 * unconditionally adjusted back in sev_es_ist_exit(). Otherwise a nested

 * sev_es_ist_exit() call may adjust back the IST entry too early.

 * unconditionally adjusted back in __sev_es_ist_exit(). Otherwise a

 * nested sev_es_ist_exit() call may adjust back the IST entry too

 * early.

 *

 * The __sev_es_ist_enter() and __sev_es_ist_exit() functions always run

 * on the NMI IST stack, as they are only called from NMI handling code

 * right now.

 */

void noinstr __sev_es_ist_enter(struct pt_regs *regs)

{

	unsigned long old_ist, new_ist;



	/* Read old IST entry */

	old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]);

	new_ist = old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]);



	/* Make room on the IST stack */

	/*

	 * If NMI happened while on the #VC IST stack, set the new IST

	 * value below regs->sp, so that the interrupted stack frame is

	 * not overwritten by subsequent #VC exceptions.

	 */

	if (on_vc_stack(regs))

		new_ist = ALIGN_DOWN(regs->sp, 8) - sizeof(old_ist);

	else

		new_ist = old_ist - sizeof(old_ist);

		new_ist = regs->sp;



	/* Store old IST entry */

	/*

	 * Reserve additional 8 bytes and store old IST value so this

	 * adjustment can be unrolled in __sev_es_ist_exit().

	 */

	new_ist -= sizeof(old_ist);

	*(unsigned long *)new_ist = old_ist;



	/* Set new IST entry */