[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/3] VMX: allocate VMCS pages from domain heap
On 24/11/15 10:55, Andrew Cooper wrote: > On 24/11/15 07:50, Jan Beulich wrote: >>>>> On 24.11.15 at 06:04, <kevin.tian@xxxxxxxxx> wrote: >>>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] >>>> Sent: Monday, November 23, 2015 10:28 PM >>>> >>>>>>> On 21.10.15 at 05:16, <kevin.tian@xxxxxxxxx> wrote: >>>>>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] >>>>>> Sent: Tuesday, October 20, 2015 6:36 PM >>>>>>>>> On 20.10.15 at 12:12, <andrew.cooper3@xxxxxxxxxx> wrote: >>>>>>> On 19/10/15 16:22, Jan Beulich wrote: >>>>>>>> @@ -580,7 +583,7 @@ int vmx_cpu_up_prepare(unsigned int cpu) >>>>>>>> void vmx_cpu_dead(unsigned int cpu) >>>>>>>> { >>>>>>>> vmx_free_vmcs(per_cpu(vmxon_region, cpu)); >>>>>>>> - per_cpu(vmxon_region, cpu) = NULL; >>>>>>>> + per_cpu(vmxon_region, cpu) = 0; >>>>>>> While this is currently safe (as pa 0 is not part of the available heap >>>>>>> allocation range), might it be worth introducing a named sentential? I >>>>>>> can forsee a DMLite nested Xen scenario where we definitely don't need >>>>>>> to treat the low 1MB magically. >>>>>> I guess there are more things to adjust if we ever cared to recover >>>>>> the few hundred kb below 1Mb. And then I don't see why nested >>>>>> Xen would matter here: One major main reason for reserving that >>>>>> space is that we want to put the trampoline there. Do you think >>>>>> DMlite would allow us to get away without? But even if so, this >>>>>> would again fall under what I've said in the first sentence. >>>>> Could you at least introduce a macro first? Regardless of how much >>>>> things to adjust, this way makes future change simple. >>>> So I've made an attempt, but this is really getting unwieldy: Setting >>>> per-CPU data to non-zero initial values is not possible; making sure >>>> cleanup code avoids assuming such variables got initialized is quite >>>> error prone. Same goes at least to a certain extent for struct vcpu >>>> members (see e.g. nvmx_vcpu_destroy(), which currently is >>>> correct no matter whether nvmx_vcpu_initialise() ran at all, or to >>>> completion). >>>> >>>> I also don't see what a macro would help here, or how/where it >>>> should be used. paddr_valid()? Yes, I could do this, but it wouldn't >>>> simplify much when later wanting to convert to a non-zero value >>>> for above reasons (it would instead give the wrong impression that >>>> changing the value is all it takes). >>>> >>> Thanks for looking into this attempt. Based on your explanation >>> I think your original code is reasonable to go. Here is my ack: >>> >>> Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx> >> Thanks Kevin. Andrew - please indicate whether your previous >> comment is to be considered a NAK, or "just a comment". > I would prefer a sentinel value being introduced, but can live without > it being changed. It is definitely not the only area which uses 0 as a > sentinel and cleanup will have to happen, one way or another. Actually it turns out that we already have an appropriate sentinel. include/asm-x86/types.h:34:#define INVALID_PADDR (~0UL) ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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