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Commit 9d2a4d71 authored by Sukadev Bhattiprolu's avatar Sukadev Bhattiprolu Committed by Michael Ellerman
Browse files

powerpc: Define set_thread_uses_vas() 



A CP_ABORT instruction is required in processes that have mapped a VAS
"paste address" with the intention of using COPY/PASTE instructions.
But since CP_ABORT is expensive, we want to restrict it to only
processes that use/intend to use COPY/PASTE.

Define an interface, set_thread_uses_vas(), that VAS can use to
indicate that the current process opened a send window. During context
switch, issue CP_ABORT only for processes that have the flag set.

Thanks for input from Nick Piggin, Michael Ellerman.

Signed-off-by: default avatarSukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
[mpe: Fix to not use new_thread after _switch() returns]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent ec233ede

arch/powerpc/include/asm/processor.h

+2 −0
Original line number Diff line number Diff line
@@ -341,7 +341,9 @@ struct thread_struct { 
	unsigned long	sier;

	unsigned long	mmcr2;

	unsigned 	mmcr0;



	unsigned 	used_ebb;

	unsigned int	used_vas;

#endif

};

arch/powerpc/include/asm/switch_to.h

+2 −0
Original line number Diff line number Diff line
@@ -91,6 +91,8 @@ static inline void clear_task_ebb(struct task_struct *t) 
#endif

}



extern int set_thread_uses_vas(void);



extern int set_thread_tidr(struct task_struct *t);

extern void clear_thread_tidr(struct task_struct *t);

arch/powerpc/kernel/process.c

+31 −10
Original line number Diff line number Diff line
@@ -1244,17 +1244,17 @@ struct task_struct *__switch_to(struct task_struct *prev, 
		 * The copy-paste buffer can only store into foreign real

		 * addresses, so unprivileged processes can not see the

		 * data or use it in any way unless they have foreign real

		 * mappings. We don't have a VAS driver that allocates those

		 * yet, so no cpabort is required.

		 */

		if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {

			/*

			 * DD1 allows paste into normal system memory, so we

			 * do an unpaired copy here to clear the buffer and

			 * prevent a covert channel being set up.

		 * mappings. If the new process has the foreign real address

		 * mappings, we must issue a cp_abort to clear any state and

		 * prevent snooping, corruption or a covert channel.

		 *

			 * cpabort is not used because it is quite expensive.

		 * DD1 allows paste into normal system memory so we do an

		 * unpaired copy, rather than cp_abort, to clear the buffer,

		 * since cp_abort is quite expensive.

		 */

		if (current_thread_info()->task->thread.used_vas) {

			asm volatile(PPC_CP_ABORT);

		} else if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {

			asm volatile(PPC_COPY(%0, %1)

					: : "r"(dummy_copy_buffer), "r"(0));

		}
@@ -1455,6 +1455,27 @@ void flush_thread(void) 
#endif /* CONFIG_HAVE_HW_BREAKPOINT */

}



int set_thread_uses_vas(void)

{

#ifdef CONFIG_PPC_BOOK3S_64

	if (!cpu_has_feature(CPU_FTR_ARCH_300))

		return -EINVAL;



	current->thread.used_vas = 1;



	/*

	 * Even a process that has no foreign real address mapping can use

	 * an unpaired COPY instruction (to no real effect). Issue CP_ABORT

	 * to clear any pending COPY and prevent a covert channel.

	 *

	 * __switch_to() will issue CP_ABORT on future context switches.

	 */

	asm volatile(PPC_CP_ABORT);



#endif /* CONFIG_PPC_BOOK3S_64 */

	return 0;

}



#ifdef CONFIG_PPC64

static DEFINE_SPINLOCK(vas_thread_id_lock);

static DEFINE_IDA(vas_thread_ida);