From: Chang S. Bae chang.seok.bae@intel.com
[ Upstream commit a401f45e38754953c9d402f8b3bc965707eecc91 ]
== Background ==
The XSTATE init code initializes all enabled and supported components. Then, the init states are saved in the init_fpstate buffer that is statically allocated in about one page.
The AMX TILE_DATA state is large (8KB) but its init state is zero. And the feature comes only with the compacted format with these established dependencies: AMX->XFD->XSAVES. So this state is excludable from init_fpstate.
== Problem ==
But the buffer is formatted to include that large state. Then, this can be the cause of a noisy splat like the below.
This came from XRSTORS for the task with init_fpstate in its XSAVE buffer. It is reproducible on AMX systems when the running kernel is built with CONFIG_DEBUG_PAGEALLOC=y and CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y:
Bad FPU state detected at restore_fpregs_from_fpstate+0x57/0xd0, reinitializing FPU registers. ... RIP: 0010:restore_fpregs_from_fpstate+0x57/0xd0 ? restore_fpregs_from_fpstate+0x45/0xd0 switch_fpu_return+0x4e/0xe0 exit_to_user_mode_prepare+0x17b/0x1b0 syscall_exit_to_user_mode+0x29/0x40 do_syscall_64+0x67/0x80 ? do_syscall_64+0x67/0x80 ? exc_page_fault+0x86/0x180 entry_SYSCALL_64_after_hwframe+0x63/0xcd
== Solution ==
Adjust init_fpstate to exclude dynamic states. XRSTORS from init_fpstate still initializes those states when their bits are set in the requested-feature bitmap.
Fixes: 2308ee57d93d ("x86/fpu/amx: Enable the AMX feature in 64-bit mode") Reported-by: Lin X Wang lin.x.wang@intel.com Signed-off-by: Chang S. Bae chang.seok.bae@intel.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Lin X Wang lin.x.wang@intel.com Link: https://lore.kernel.org/r/20220824191223.1248-4-chang.seok.bae@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/fpu/xstate.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index f5ef78633b4c..e77cabfa802f 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -857,9 +857,12 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) update_regset_xstate_info(fpu_user_cfg.max_size, fpu_user_cfg.max_features);
- /* Bring init_fpstate size and features up to date */ - init_fpstate.size = fpu_kernel_cfg.max_size; - init_fpstate.xfeatures = fpu_kernel_cfg.max_features; + /* + * init_fpstate excludes dynamic states as they are large but init + * state is zero. + */ + init_fpstate.size = fpu_kernel_cfg.default_size; + init_fpstate.xfeatures = fpu_kernel_cfg.default_features;
if (init_fpstate.size > sizeof(init_fpstate.regs)) { pr_warn("x86/fpu: init_fpstate buffer too small (%zu < %d), disabling XSAVE\n",