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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Is there any way to read msr in hypervisor code?
On Tue, Feb 27, 2018 at 8:25 PM, Minjun Hong <nickeysgo@xxxxxxxxx> wrote: > > Ah! Now I understand what you said. > Thank you so much, Andrew. > > BTW, isn't it possible to use PERFEVTSELx MSR in Xen directly? I eagerly want > to achieve the number of cache-misses. If you just want to monitor the number of cache misses, you can use perf in Xen: https://wiki.xenproject.org/wiki/Xen_Profiling:_oprofile_and_perf You need to enable the vpmu at the boot command. If you plan to add your own features, you can check how vpmu is implemented, which may help you implement your own feature. Best Regards, Meng ----------- Meng Xu Ph.D. Candidate in Computer and Information Science University of Pennsylvania http://www.cis.upenn.edu/~mengxu/ > > > On Tue, Feb 27, 2018 at 11:03 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> > wrote: >> >> On 27/02/18 12:35, Minjun Hong wrote: >> >> On Tue, Feb 27, 2018 at 7:00 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> >> wrote: >>> >>> On 27/02/2018 09:37, Minjun Hong wrote: >>> >>> Hello, I've tried to read msr in hypervisor code: >>> >>>> uint64_t reg; >>>> >>>> rdmsr_safe(0x412e, ret); >>> >>> >>> But, I all failed to read it because the hypervisor is running in ring-1 >>> CPL as I did googling. >>> >>> >>> Xen runs in ring 0, root mode. Forget terms like "ring -1" because they >>> are not accurate, and not a helpful description of what is going on. >>> >>> When I accessed msr, the crash log is below: >>> >>> >>>>> (XEN) ----[ Xen-4.9.0 x86_64 debug=n Not tainted ]---- >>>>> >>>>> (XEN) CPU: 7 >>>>> >>>>> (XEN) RIP: e008:[<ffff82d08024139d>] >>>>> mcsched.c#shscan_timer_fn+0xd/0x180 >>>>> >>>>> (XEN) RFLAGS: 0000000000010206 CONTEXT: hypervisor >>>>> >>>>> (XEN) rax: ffff83084abfe028 rbx: ffff83084abfe300 rcx: >>>>> 000000000000412e >>>>> >>>>> (XEN) rdx: ffff83084abb7fff rsi: ffff82d080632f00 rdi: >>>>> 0000000000000000 >>>>> >>>>> (XEN) rbp: ffff82d080241390 rsp: ffff83084abb7e30 r8: >>>>> ffff830868d4bdc0 >>>>> >>>>> (XEN) r9: 0000000000000005 r10: 0000012da75b50a5 r11: >>>>> ffff8300782f3060 >>>>> >>>>> (XEN) r12: 0000000000000000 r13: 0000012d9f9d6e07 r14: >>>>> ffff83084abb7fff >>>>> >>>>> (XEN) r15: ffff82d08062ad80 cr0: 000000008005003b cr4: >>>>> 00000000003526e0 >>>>> >>>>> (XEN) cr3: 00000003426f3000 cr2: 00007fc3c21d4000 >>>>> >>>>> (XEN) ds: 0000 es: 0000 fs: 0000 gs: 0000 ss: e010 cs: e008 >>>>> >>>>> (XEN) Xen code around <ffff82d08024139d> >>>>> (mcsched.c#shscan_timer_fn+0xd/0x180): >>>>> >>>>> (XEN) 00 00 41 55 41 54 55 53 <0f> 32 4c 8d 05 0a 79 11 00 48 8d 0d 91 >>>>> 45 14 00 >>> >>> >>> This is a rdmsr(), not rdmsr_safe(), which is why you are crashing. >>> >>> Irrespective of that, 0x412e isn't an MSR which exists on any real >>> hardware, so I'm not sure what other result you were expecting. >>> >>> ~Andrew >> >> >> Thanks for your answer, Andrew. >> >> Actually, I intended to get the number of cache-misses from msr and >> according to "Figure 18-1 Layout of IA32_PERFEVTSELx MSRs in Intel® 64 and >> IA-32 Architectures Software Developer’s Manual Volume 3B: System >> Programming Guide", >> it can be achieved by "0x412e": >> >> Bit Position >> >> CPUID.AH.EBX >> >> Event Name >> >> UMask >> >> Event Select >> >> 0 >> >> UnHalted Core Cycles >> >> 00H >> >> 3CH >> >> 1 >> >> Instruction Retired >> >> 00H >> >> C0H >> >> 2 >> >> UnHalted Reference Cycles >> >> 01H >> >> 3CH >> >> 3 >> >> LLC Reference >> >> 4FH >> >> 2EH >> >> 4 >> >> LLC Misses >> >> 41H >> >> 2EH >> >> 5 >> >> Branch Instruction Retired >> >> 00H >> >> C4H >> >> 6 >> >> Branch Misses Retired >> >> 00H >> >> C5H >> >> >> I also tried to do that w/ rdmsr_safe() but, I failed to read msr. >> Through the macro that returns a non-zero value, it was easy to see that >> reading msr failed: >> >>> if ( rdmsr_safe(0x412e, ret) ) { >>> printk("cannot read msr!!!\n"); >>> } else { >>> printk("rdmsr: %lu\n", ret); >>> } >> >> >> I cannot understand why you said "0x412e isn't an MSR which exists on any >> real hardware" so, is it impossible to get the number of cache-misses by >> using msr ?? >> >> >> The bit you highlight above are values you need to write into one of the >> PERFEVTSELx MSRs, to cause hardware to track that event. It does not mean >> MSR by that index exists. >> >> ~Andrew > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@xxxxxxxxxxxxxxxxxxxx > https://lists.xenproject.org/mailman/listinfo/xen-devel _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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