From 5740b8b0f3c7fcbd3a2fa33b47e57afc9c8bcef7 Mon Sep 17 00:00:00 2001 From: Bernhard Kaindl Date: Tue, 16 Jun 2026 14:15:30 +0200 Subject: [PATCH] x86/efi: Skip FPU save/restore for idle vCPU in EFI runtime path MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Anthony reported a boot-time assertion in init_xen_time() via efi_get_time() -> efi_rs_enter() in vcpu_save_fpu() on a Broadwell-D system: Assertion '!is_idle_vcpu(v)' failed at arch/x86/i387.c:195 This became fragile after the lazy-FPU removal cleanup series: In 1792bb9a99d2 ("x86: Cleanup cr0.TS flag handling"), efi_rs_enter() was changed from save_fpu_enable() to vcpu_save_fpu(curr), which unconditionally asserts !is_idle_vcpu(v) so an EFI runtime call in idle context now asserts. Likewise, in dba44e051209 ("x86: Remove fully_eager_fpu"), efi_rs_leave() was changed to call vcpu_restore_fpu(curr), which has the same assertion and can fail for the same reason. Guard both EFI runtime FPU calls with !is_idle_vcpu() to skip save/restore for idle vCPUs, which don't have an FPU context to save/restore, much like the calls are guarded in __context_switch(), where save/restore is done only for non-idle vCPUs. Fixes: 1792bb9a99d2 ("x86: Cleanup cr0.TS flag handling") Fixes: dba44e051209 ("x86: Remove fully_eager_fpu") Reported-by: Anthony PERARD Suggested-by: Jan Beulich Signed-off-by: Bernhard Kaindl Tested-by: Anthony PERARD Acked-by: Marek Marczykowski-Górecki Release-Acked-by: Oleksii Kurochko --- xen/common/efi/runtime.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c index a23fa75e37..596f2710fb 100644 --- a/xen/common/efi/runtime.c +++ b/xen/common/efi/runtime.c @@ -98,7 +98,8 @@ struct efi_rs_state efi_rs_enter(void) */ sync_local_execstate(); state.cr3 = read_cr3(); - vcpu_save_fpu(current); + if ( !is_idle_vcpu(current) ) + vcpu_save_fpu(current); asm volatile ( "fnclex; fldcw %0" :: "m" (fcw) ); asm volatile ( "ldmxcsr %0" :: "m" (mxcsr) ); @@ -159,7 +160,8 @@ void efi_rs_leave(struct efi_rs_state *state) } irq_exit(); spin_unlock(&efi_rs_lock); - vcpu_restore_fpu(curr); + if ( !is_idle_vcpu(curr) ) + vcpu_restore_fpu(curr); } unsigned long efi_get_time(void)