Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is enabled

[kernel test robot]

Hi Sean,

I love your patch! Yet something to improve:

[auto build test ERROR on tip/auto-latest]
[also build test ERROR on v5.9-rc1 next-20200821]
[cannot apply to tip/x86/asm luto/next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Sean-Christopherson/x86-entry-64-Disallow-RDPID-in-paranoid-entry-if-KVM-is-enabled/20200821-105339
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git a9bd3a91d6e49ebd2d7d8ace91d4cc339c382a31
config: x86_64-randconfig-a005-20200820 (attached as .config)
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project b587ca93be114d07ec3bf654add97d7872325281)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All errors (new ones prefixed by >>):

   arch/x86/entry/entry_64.S: Assembler messages:
>> arch/x86/entry/entry_64.S:851: Error: too many positional arguments
   clang-12: error: assembler command failed with exit code 1 (use -v to see invocation)

# https://github.com/0day-ci/linux/commit/bebb51882f9c18938e44b6a7b66fdf0452eea142
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Sean-Christopherson/x86-entry-64-Disallow-RDPID-in-paranoid-entry-if-KVM-is-enabled/20200821-105339
git checkout bebb51882f9c18938e44b6a7b66fdf0452eea142
vim +851 arch/x86/entry/entry_64.S

   794	
   795	/*
   796	 * Save all registers in pt_regs. Return GSBASE related information
   797	 * in EBX depending on the availability of the FSGSBASE instructions:
   798	 *
   799	 * FSGSBASE	R/EBX
   800	 *     N        0 -> SWAPGS on exit
   801	 *              1 -> no SWAPGS on exit
   802	 *
   803	 *     Y        GSBASE value at entry, must be restored in paranoid_exit
   804	 */
   805	SYM_CODE_START_LOCAL(paranoid_entry)
   806		UNWIND_HINT_FUNC
   807		cld
   808		PUSH_AND_CLEAR_REGS save_ret=1
   809		ENCODE_FRAME_POINTER 8
   810	
   811		/*
   812		 * Always stash CR3 in %r14.  This value will be restored,
   813		 * verbatim, at exit.  Needed if paranoid_entry interrupted
   814		 * another entry that already switched to the user CR3 value
   815		 * but has not yet returned to userspace.
   816		 *
   817		 * This is also why CS (stashed in the "iret frame" by the
   818		 * hardware at entry) can not be used: this may be a return
   819		 * to kernel code, but with a user CR3 value.
   820		 *
   821		 * Switching CR3 does not depend on kernel GSBASE so it can
   822		 * be done before switching to the kernel GSBASE. This is
   823		 * required for FSGSBASE because the kernel GSBASE has to
   824		 * be retrieved from a kernel internal table.
   825		 */
   826		SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14
   827	
   828		/*
   829		 * Handling GSBASE depends on the availability of FSGSBASE.
   830		 *
   831		 * Without FSGSBASE the kernel enforces that negative GSBASE
   832		 * values indicate kernel GSBASE. With FSGSBASE no assumptions
   833		 * can be made about the GSBASE value when entering from user
   834		 * space.
   835		 */
   836		ALTERNATIVE "jmp .Lparanoid_entry_checkgs", "", X86_FEATURE_FSGSBASE
   837	
   838		/*
   839		 * Read the current GSBASE and store it in %rbx unconditionally,
   840		 * retrieve and set the current CPUs kernel GSBASE. The stored value
   841		 * has to be restored in paranoid_exit unconditionally.
   842		 *
   843		 * The MSR write ensures that no subsequent load is based on a
   844		 * mispredicted GSBASE. No extra FENCE required.
   845		 *
   846		 * Disallow RDPID if KVM is enabled as it may consume a guest's TSC_AUX
   847		 * if an NMI arrives in KVM's run loop.  KVM loads guest's TSC_AUX on
   848		 * VM-Enter and may not restore the host's value until the CPU returns
   849		 * to userspace, i.e. KVM depends on the kernel not using TSC_AUX.
   850		 */
 > 851		SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx no_rdpid=IS_ENABLED(CONFIG_KVM)
   852		ret
   853	

---
0-DAY CI Kernel Test Service, Intel Corporation
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