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author | Herbert Xu <herbert@gondor.apana.org.au> | 2015-06-19 22:07:07 +0800 |
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committer | Herbert Xu <herbert@gondor.apana.org.au> | 2015-06-19 22:07:07 +0800 |
commit | c0b59fafe31bf91f589736be304d739b13952fdd (patch) | |
tree | 0088a41c6b68132739294643be06734e3af67677 /arch/x86/kernel/process_64.c | |
parent | 28bceeaaf81140d69647acd0eb7dc9312f27844a (diff) | |
parent | bfa1ce5f38938cc9e6c7f2d1011f88eba2b9e2b2 (diff) | |
download | blackbird-obmc-linux-c0b59fafe31bf91f589736be304d739b13952fdd.tar.gz blackbird-obmc-linux-c0b59fafe31bf91f589736be304d739b13952fdd.zip |
Merge branch 'mvebu/drivers' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
Merge the mvebu/drivers branch of the arm-soc tree which contains
just a single patch bfa1ce5f38938cc9e6c7f2d1011f88eba2b9e2b2 ("bus:
mvebu-mbus: add mv_mbus_dram_info_nooverlap()") that happens to be
a prerequisite of the new marvell/cesa crypto driver.
Diffstat (limited to 'arch/x86/kernel/process_64.c')
-rw-r--r-- | arch/x86/kernel/process_64.c | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 4baaa972f52a..ddfdbf74f174 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -419,6 +419,34 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV)) __switch_to_xtra(prev_p, next_p, tss); + if (static_cpu_has_bug(X86_BUG_SYSRET_SS_ATTRS)) { + /* + * AMD CPUs have a misfeature: SYSRET sets the SS selector but + * does not update the cached descriptor. As a result, if we + * do SYSRET while SS is NULL, we'll end up in user mode with + * SS apparently equal to __USER_DS but actually unusable. + * + * The straightforward workaround would be to fix it up just + * before SYSRET, but that would slow down the system call + * fast paths. Instead, we ensure that SS is never NULL in + * system call context. We do this by replacing NULL SS + * selectors at every context switch. SYSCALL sets up a valid + * SS, so the only way to get NULL is to re-enter the kernel + * from CPL 3 through an interrupt. Since that can't happen + * in the same task as a running syscall, we are guaranteed to + * context switch between every interrupt vector entry and a + * subsequent SYSRET. + * + * We read SS first because SS reads are much faster than + * writes. Out of caution, we force SS to __KERNEL_DS even if + * it previously had a different non-NULL value. + */ + unsigned short ss_sel; + savesegment(ss, ss_sel); + if (ss_sel != __KERNEL_DS) + loadsegment(ss, __KERNEL_DS); + } + return prev_p; } |