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powerpc: Define set_thread_uses_vas()

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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: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
[mpe: Fix to not use new_thread after _switch() returns]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Sukadev Bhattiprolu 2017-11-07 18:23:54 -08:00 committed by Michael Ellerman
parent ec233ede4c
commit 9d2a4d7133
3 changed files with 35 additions and 10 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
arch/powerpc/include/asm/processor.h
View file

@ -341,7 +341,9 @@ struct thread_struct {
unsigned long sier;
unsigned long mmcr2;
unsigned mmcr0;
unsigned used_ebb;
unsigned int used_vas;
#endif
};

2
arch/powerpc/include/asm/switch_to.h
View file

@ -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);

41
arch/powerpc/kernel/process.c
View file

@ -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.
* 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.
*
* 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 (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.
*
* cpabort is not used because it 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);