On 12/10/2018 02:59 PM, Catalin Marinas wrote:
On Fri, Dec 07, 2018 at 08:38:11AM +0000, Julien Thierry wrote:
On 12/06/2018 06:25 PM, Catalin Marinas wrote:
On Mon, Dec 03, 2018 at 01:55:18PM +0000, Julien Thierry wrote:
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 07c3408..cabfcae 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -233,6 +233,23 @@ static inline void uaccess_enable_not_uao(void)
__uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
}
+#define unsafe_user_region_active uaccess_region_active
+static inline bool uaccess_region_active(void)
+{
+ if (system_uses_ttbr0_pan()) {
+ u64 ttbr;
+
+ ttbr = read_sysreg(ttbr1_el1);
+ return ttbr & TTBR_ASID_MASK;
Nitpick: could write this in 1-2 lines.
True, I can do that in 1 line.
+ } else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO)) {
+ return (read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN) ?
+ false :
+ !read_sysreg_s(SYS_PSTATE_PAN);
+ }
ARM64_ALT_PAN_NOT_UAO implies ARM64_HAS_PAN which implies SCTLR_EL1.SPAN
is 0 at run-time. Is this to cope with the case of being called prior to
cpu_enable_pan()?
Yes, the issue I can into is that for cpufeatures, .cpu_enable() callbacks
are called inside stop_machine() which obviously might_sleep and so attempts
to check whether user_access is on. But for features that get enabled before
PAN, the PAN bit will be set.
OK, so the PSTATE.PAN bit only makes sense when SCTLR_EL1.SPAN is 0, IOW
the PAN hardware feature has been enabled. Maybe you could write it
(together with some comment):
} else if (cpus_have_const_cap(ARM64_ALT_PAN_NOT_UAO) &&
!(read_sysreg(sctlr_el1) & SCTLR_EL1_SPAN)) {
/* only if PAN is present and enabled */
return !read_sysreg_s(SYS_PSTATE_PAN)
}
On the cpufeature.c side of things, it seems that we enable the
static_branch before calling the cpu_enable. I wonder whether changing
the order here would help with avoid the SCTLR_EL1 read (not sure what
else it would break; cc'ing Suzuki).
I doubt if we would gain anything by moving it around.
cpus_have_const_cap() would fall back to test_bit() until we mark that
the static_branches have been updated explicitly, which happens after
we have issued the stop_machine(). So, even if we move the static branch
per capability, we don't gain much.
Is that what you were looking for ?
Cheers
Suzuki
