[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 06/25] libelf-loader: introduce elf_load_image
>>> On 09.12.11 at 14:40, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote: > On Fri, 2011-12-09 at 13:33 +0000, Jan Beulich wrote: >> >>> On 09.12.11 at 14:13, <stefano.stabellini@xxxxxxxxxxxxx> wrote: >> > Implement a new function, called elf_load_image, to perform the actually >> > copy of the elf image and clearing the padding. >> > The function is implemented as memcpy and memset when the library is >> > built as part of the tools, but it is implemented as copy_to_user and >> > clear_user when built as part of Xen, so that it can be safely called >> > with an HVM style dom0. >> >> I meant to ask this on the first round already, but apparently forgot: >> What is it that prevents memcpy()/memset() from being used for a >> HVM style Dom0? {clear,copy_to}_user() still expect the guest memory >> to be visible in the hypervisor's virtual address space - how could a >> fault happen here? And if you have to take precautions for a fault, >> shouldn't the calling code check the respective return values? > > HVM guest memory is not (necessarily) mapped in the hypervisor page > tables, it needs to be mapped on demand. Also the source/target (delete > as appropriate) is a guest virtual address so even if the RAM happened > to be mapped it would (likely) not be in the same place so at a minimum > we need to translate things. > > This is what copy_{to,from}_user does for an HVM guest even on X86, > where copy_to_user becomes copy_to_user_hvm as appropriate. But that's not true - the distinction of hvm vs pv is at the copy_to_guest() layer (raw_copy_to_guest() in the x86 case). So maybe the patch meant to use those interfaces (and then we'd need a clear_guest() too, which should also have been obvious by the fact that the prior patch only introduced clear_user(), but no hvm variant of it)? Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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