[PATCH v3 04/13] arm64: alternatives: use tpidr_el2 on VHE hosts

James Morse
2017-09-22T18:26:05Z

Now that KVM uses tpidr_el2 in the same way as Linux's cpu_offset in
tpidr_el1, merge the two. This saves KVM from save/restoring tpidr_el1
on VHE hosts, and allows future code to blindly access per-cpu variables
without triggering world-switch.

Signed-off-by: James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>
Reviewed-by: Christoffer Dall <cdall-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
---
Changes since v1:
* cpu_copy_el2regs()'s 'have I been patched' test now always sets a register,
just in case the compiler optimises out part of the logic.

arch/arm64/include/asm/assembler.h | 8 ++++++++
arch/arm64/include/asm/percpu.h | 11 +++++++++--
arch/arm64/include/asm/processor.h | 1 +
arch/arm64/kernel/cpufeature.c | 23 +++++++++++++++++++++++
arch/arm64/mm/proc.S | 8 ++++++++
5 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index d58a6253c6ab..1ba12f59dec0 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -242,7 +242,11 @@ lr .req x30 // link register
#else
adr_l \dst, \sym
#endif
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
mrs \tmp, tpidr_el1
+alternative_else
+ mrs \tmp, tpidr_el2
+alternative_endif
add \dst, \dst, \tmp
.endm

@@ -253,7 +257,11 @@ lr .req x30 // link register
*/
.macro ldr_this_cpu dst, sym, tmp
adr_l \dst, \sym
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
mrs \tmp, tpidr_el1
+alternative_else
+ mrs \tmp, tpidr_el2
+alternative_endif
ldr \dst, [\dst, \tmp]
.endm

diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h
index 3bd498e4de4c..43393208229e 100644
--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -16,11 +16,15 @@
#ifndef __ASM_PERCPU_H
#define __ASM_PERCPU_H

+#include <asm/alternative.h>
#include <asm/stack_pointer.h>

static inline void set_my_cpu_offset(unsigned long off)
{
- asm volatile("msr tpidr_el1, %0" :: "r" (off) : "memory");
+ asm volatile(ALTERNATIVE("msr tpidr_el1, %0",
+ "msr tpidr_el2, %0",
+ ARM64_HAS_VIRT_HOST_EXTN)
+ :: "r" (off) : "memory");
}

static inline unsigned long __my_cpu_offset(void)
@@ -31,7 +35,10 @@ static inline unsigned long __my_cpu_offset(void)
* We want to allow caching the value, so avoid using volatile and
* instead use a fake stack read to hazard against barrier().
*/
- asm("mrs %0, tpidr_el1" : "=r" (off) :
+ asm(ALTERNATIVE("mrs %0, tpidr_el1",
+ "mrs %0, tpidr_el2",
+ ARM64_HAS_VIRT_HOST_EXTN)
+ : "=r" (off) :
"Q" (*(const unsigned long *)current_stack_pointer));

return off;
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 29adab8138c3..8f2d0f7d193b 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -193,5 +193,6 @@ static inline void spin_lock_prefetch(const void *ptr)

int cpu_enable_pan(void *__unused);
int cpu_enable_cache_maint_trap(void *__unused);
+int cpu_copy_el2regs(void *__unused);

#endif /* __ASM_PROCESSOR_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index cd52d365d1f0..8e4c7da2b126 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -865,6 +865,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.capability = ARM64_HAS_VIRT_HOST_EXTN,
.def_scope = SCOPE_SYSTEM,
.matches = runs_at_el2,
+ .enable = cpu_copy_el2regs,
},
{
.desc = "32-bit EL0 Support",
@@ -1308,3 +1309,25 @@ static int __init enable_mrs_emulation(void)
}

late_initcall(enable_mrs_emulation);
+
+int cpu_copy_el2regs(void *__unused)
+{
+ int do_copyregs = 0;
+
+ /*
+ * Copy register values that aren't redirected by hardware.
+ *
+ * Before code patching, we only set tpidr_el1, all CPUs need to copy
+ * this value to tpidr_el2 before we patch the code. Once we've done
+ * that, freshly-onlined CPUs will set tpidr_el2, so we don't need to
+ * do anything here.
+ */
+ asm volatile(ALTERNATIVE("mov %0, #1", "mov %0, #0",
+ ARM64_HAS_VIRT_HOST_EXTN)
+ : "=r" (do_copyregs) : : );
+
+ if (do_copyregs)
+ write_sysreg(read_sysreg(tpidr_el1), tpidr_el2);
+
+ return 0;
+}
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 877d42fb0df6..109d43a15aaf 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -70,7 +70,11 @@ ENTRY(cpu_do_suspend)
mrs x8, mdscr_el1
mrs x9, oslsr_el1
mrs x10, sctlr_el1
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
mrs x11, tpidr_el1
+alternative_else
+ mrs x11, tpidr_el2
+alternative_endif
mrs x12, sp_el0
stp x2, x3, [x0]
stp x4, xzr, [x0, #16]
@@ -116,7 +120,11 @@ ENTRY(cpu_do_resume)
msr mdscr_el1, x10

msr sctlr_el1, x12
+alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
msr tpidr_el1, x13
+alternative_else
+ msr tpidr_el2, x13
+alternative_endif
msr sp_el0, x14
/*
* Restore oslsr_el1 by writing oslar_el1