[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] x86/hvm: honor guest's option when updating secondary system time for guest
>>> On 25.07.14 at 06:30, <feng.wu@xxxxxxxxx> wrote: > >> -----Original Message----- >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] >> Sent: Wednesday, July 23, 2014 8:19 PM >> To: Wu, Feng >> Cc: linux@xxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxx; konrad.wilk@xxxxxxxxxx; >> keir@xxxxxxx; tim@xxxxxxx >> Subject: Re: [PATCH 2/2] x86/hvm: honor guest's option when updating >> secondary system time for guest >> >> >>> On 08.07.14 at 01:18, <feng.wu@xxxxxxxxx> wrote: >> > --- a/xen/include/public/vcpu.h >> > +++ b/xen/include/public/vcpu.h >> > @@ -227,6 +227,16 @@ struct vcpu_register_time_memory_area { >> > typedef struct vcpu_register_time_memory_area >> > vcpu_register_time_memory_area_t; >> > DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t); >> > >> > +/* >> > + * Flags to tell Xen whether we need to do the SMAP check when updating >> > + * the secondary copy of the vcpu time when SMAP is enabled. Since the >> > + * memory location for the secondary copy of the vcpu time may be mapped >> > + * into userspace by guests intendedly, we let the guest to determine >> > + * whether the check is needed. The default behavior of hypevisor is >> > + * not doing the check. >> > + */ >> > +#define VCPUOP_enable_smap_check_vcpu_time_memory_area 14 >> >> I think the new op to be VCPUOP_register_vcpu_time_memory_area_smap, >> identical to VCPUOP_register_vcpu_time_memory_area apart from also >> setting the flag, would be more natural. But considering what I just wrote >> in the reply to Tim I guess we can expect a nun-user mapping to be >> presented here anyway, i.e. we wouldn't need to new operation at all. > > Do you mean since the user-paging is r/o, guest will pass a r/w kernel page > to > Xen for updating the system time. So we don't need to do the SMAP check > in this case? If the user page is r/o, it's VA obviously can't be used for updating by Xen. Hence the kernel has to provide a r/w mapped VA. That should be subject to SMAP checking (consistent with the runstate area handling), to make sure it's not a user accessible mapping. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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