----- 22 cze 2020 o 18:16, Jan Beulich jbeul...@suse.com napisał(a): > On 22.06.2020 18:02, Michał Leszczyński wrote: >> ----- 22 cze 2020 o 17:22, Jan Beulich jbeul...@suse.com napisał(a): >>> On 22.06.2020 16:35, Michał Leszczyński wrote: >>>> ----- 22 cze 2020 o 15:25, Jan Beulich jbeul...@suse.com napisał(a): >>>>> Is any of what you do in this switch() actually legitimate without >>>>> hvm_set_vmtrace_pt_size() having got called for the guest? From >>>>> remarks elsewhere I imply you expect the param that you currently >>>>> use to be set upon domain creation time, but at the very least the >>>>> potentially big buffer should imo not get allocated up front, but >>>>> only when tracing is to actually be enabled. >>>> >>>> Wait... so you want to allocate these buffers in runtime? >>>> Previously we were talking that there is too much runtime logic >>>> and these enable/disable hypercalls should be stripped to absolute >>>> minimum. >>> >>> Basic arrangements can be made at domain creation time. I don't >>> think though that it would be a good use of memory if you >>> allocated perhaps many gigabytes of memory just for possibly >>> wanting to enable tracing on a guest. >>> >> >> From our previous conversations I thought that you want to have >> as much logic moved to the domain creation as possible. >> >> Thus, a parameter "vmtrace_pt_size" was introduced. By default it's >> zero (= disabled), if you set it to a non-zero value, then trace buffers >> of given size will be allocated for the domain and you have possibility >> to use ipt_enable/ipt_disable at any moment. >> >> This way the runtime logic is as thin as possible. I assume user knows >> in advance whether he/she would want to use external monitoring with IPT >> or not. > > Andrew - I think you requested movement to domain_create(). Could > you clarify if indeed you mean to also allocate the big buffers > this early? > >> It's also not "many gigabytes". In most use cases a buffer of 16/32/64 MB >> would suffice, I think. > > But that one such buffer per vCPU, isn't it? Plus these buffers > need to be physically contiguous, which is an additional possibly > severe constraint.
Yes. For my use case (VMI stuff) I estimate 16-64 MB per vCPU and for fuzzing I think it would be even less. And also yes - these buffers need to be physically contigous and aligned because otherwise CPU would refuse to use them. Best regards, Michał Leszczyński CERT Polska
