linux-kernel - Re: [Kernel BUG?] SMSW operation get success on UMIP KVM guest

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Date:   Mon, 1 Jul 2019 10:03:28 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Li Wang <liwang@...hat.com>
cc:     ricardo.neri-calderon@...ux.intel.com, pbonzini@...hat.com,
        kernellwp@...il.com, ricardo.neri@...el.com, pengfei.xu@...el.com,
        LTP List <ltp@...ts.linux.it>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ping Fang <pifang@...hat.com>
Subject: Re: [Kernel BUG?] SMSW operation get success on UMIP KVM guest

On Mon, 1 Jul 2019, Li Wang wrote:

> Hello there,
> 
> LTP/umip_basic_test get failed on KVM UMIP system(kernel-v5.2-rc4.x86_64).
> The test is only trying to do
>      asm volatile("smsw %0\n" : "=m" (val));
> and expect to get SIGSEGV in this SMSW operation, but it exits with 0
> unexpectedly.
> 
> ====================
> # grep CONFIG_X86_INTEL_UMIP /boot/config-5.2.0-0.rc4.x86_64
> CONFIG_X86_INTEL_UMIP=y
> 
> # lscpu |grep umip
> Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp
> lm constant_tsc rep_good nopl xtopology cpuid tsc_known_freq pni pclmulqdq
> ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer
> aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch cpuid_fault
> invpcid_single pti ssbd ibrs ibpb stibp fsgsbase tsc_adjust bmi1 hle avx2
> smep bmi2 erms invpcid rtm mpx avx512f avx512dq rdseed adx smap clflushopt
> clwb avx512cd avx512bw avx512vl xsaveopt xsavec xgetbv1 xsaves arat umip
> pku ospke md_clear
> 
> # ./umip_basic_test
> ...
> umip_basic_test.c:68: INFO: TEST smsw, smsw result save at [0x7ffda00dca70]
> umip_basic_test.c:118: FAIL: Didn't receive SIGSEGV, child exited with
> exited with 0

SMSW is emulated and returns a constant value:

#define CR0_STATE       (X86_CR0_PE | X86_CR0_MP | X86_CR0_ET | \
                         X86_CR0_NE | X86_CR0_WP | X86_CR0_AM | \
                         X86_CR0_PG)

IIRC that is done to not break stuff like Wine. Ricardo should know the
details.

Thanks,

	tglx