[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
> 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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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