[Xen-devel] [PATCH 2/2] xen/arm: don't enable VFP on XEN during the boot

[Julien Grall <julien.grall@xxxxxxxxxx>]

We can safely remove VFP support in XEN because:
    - the guest will enable VFP support when a process requires it
    - XEN doesn't use VFP

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 xen/arch/arm/Rules.mk     |    2 +-
 xen/arch/arm/setup.c      |    2 --
 xen/arch/arm/smpboot.c    |    1 -
 xen/include/asm-arm/vfp.h |   28 ----------------------------
 4 files changed, 1 insertion(+), 32 deletions(-)

diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
index 422ed04..a18e7fd 100644
--- a/xen/arch/arm/Rules.mk
+++ b/xen/arch/arm/Rules.mk
@@ -22,7 +22,7 @@ arm := y
 ifeq ($(TARGET_SUBARCH),arm32)
 # Prevent floating-point variables from creeping into Xen.
 CFLAGS += -msoft-float
-CFLAGS += -mcpu=cortex-a15 -mfpu=vfpv3 -mfloat-abi=softfp
+CFLAGS += -mcpu=cortex-a15
 arm32 := y
 arm64 := n
 endif
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index da2a734..2df091e 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -457,8 +457,6 @@ void __init start_xen(unsigned long boot_phys_offset,
 
     setup_virt_paging();
 
-    enable_vfp();
-
     softirq_init();
 
     tasklet_subsys_init();
diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
index 8011987..67e20d0 100644
--- a/xen/arch/arm/smpboot.c
+++ b/xen/arch/arm/smpboot.c
@@ -153,7 +153,6 @@ void __cpuinit start_secondary(unsigned long 
boot_phys_offset,
     setup_virt_paging();
 
     mmu_init_secondary_cpu();
-    enable_vfp();
 
     gic_init_secondary_cpu();
 
diff --git a/xen/include/asm-arm/vfp.h b/xen/include/asm-arm/vfp.h
index 6ba3cd1..fcffdf2 100644
--- a/xen/include/asm-arm/vfp.h
+++ b/xen/include/asm-arm/vfp.h
@@ -11,34 +11,6 @@
 # error "Unknown ARM variant"
 #endif
 
-#ifdef CONFIG_ARM_32
-
-#define FPEXC_EN (1u << 30)
-
-/* Save and restore FP state.
- * Ought to be using the new vmrs/vmsr names, but older binutils has a
- * bug where it only allows them to target fpscr (and not, say, fpexc). */
-#define READ_FP(reg) ({                                 \
-    uint32_t val;                                       \
-    asm volatile ("fmrx %0, fp" #reg : "=r" (val));     \
-    val; })
-
-#define WRITE_FP(reg, val) do {                         \
-    asm volatile ("fmxr fp" #reg ", %0" : : "r" (val)); \
-} while (0)
-
-/* Start-of-day: Turn on VFP */
-static inline void enable_vfp(void)
-{
-    WRITE_FP(exc, READ_FP(exc) | FPEXC_EN);
-}
-#else
-static inline void enable_vfp(void)
-{
-    /* Always enable on 64-bit */
-}
-#endif
-
 void vfp_save_state(struct vcpu *v);
 void vfp_restore_state(struct vcpu *v);
 
-- 
1.7.10.4


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