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x86/fpu: Exclude dynamic states from init_fpstate
[ Upstream commita401f45e38
] == 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:2308ee57d9
("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>
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1 changed files with 6 additions and 3 deletions
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@ -857,9 +857,12 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
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update_regset_xstate_info(fpu_user_cfg.max_size,
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fpu_user_cfg.max_features);
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/* Bring init_fpstate size and features up to date */
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init_fpstate.size = fpu_kernel_cfg.max_size;
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init_fpstate.xfeatures = fpu_kernel_cfg.max_features;
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/*
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* init_fpstate excludes dynamic states as they are large but init
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* state is zero.
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*/
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init_fpstate.size = fpu_kernel_cfg.default_size;
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init_fpstate.xfeatures = fpu_kernel_cfg.default_features;
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if (init_fpstate.size > sizeof(init_fpstate.regs)) {
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pr_warn("x86/fpu: init_fpstate buffer too small (%zu < %d), disabling XSAVE\n",
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