On Jul 22, 2013, at 5:38 PM, "stanley.ganyezu" <stanley.gany...@gmail.com> wrote:
> Thanks for Andrew and Brian. Do somebody ever succeed before? > It works fine in an emulator or VM, but if you run on real hardware without memory (at least t he ones I tried) the processor crashes if the page tables are in FLASH or CAR. For Itanium and Aarch64 it is possible to have a 64-bit PEI, so most of the generic code is 64-bit clean. Thanks, Andrew Fish > -----邮件原件----- > 发件人: Andrew Fish [mailto:af...@apple.com] > 发送时间: 2013年7月23日 7:36 > 收件人: Brian J. Johnson > 抄送: stanley.ganyezu; edk2-devel@lists.sourceforge.net > 主题: Re: [edk2] switch to 64 bit mode at PEI phase in X86 > > Most of the X64 (x86_64) processors I know about crash and die hard if you > place page tables in the Cache as RAM or the FLASH. That is why you see IA32 > PEI and X64 DXE on this class of systems. > > It is possible to use PAE in IA32 mode to access memory above 4 GB, > http://en.wikipedia.org/wiki/Physical_Address_Extension > > Thanks, > > Andrew Fish > > > On Jul 22, 2013, at 3:16 PM, "Brian J. Johnson" <bjohn...@sgi.com> wrote: > >> On 07/22/2013 08:55 AM, stanley.ganyezu wrote: >>> Hi Everyone, >>> >>> I want to access address above 4Gb at PEI phase in X86. Can we >>> switch to 64 bit mode before MRC? >> >> I wouldn't call myself a real expert on X86 addressing modes, but here >> are some thoughts: >> >> AFAIK the PEI core and common modules work just fine in 64-bit mode. So >> that's good. >> >> If you don't have RAM available, i.e. if you're running on real hardware >> as opposed to a virtual machine or emulator, switching to 64-bit mode >> may be difficult. Running C code before RAM is initialized requires >> putting the CPU in cache-as-RAM mode, where it uses the CPU caches as a >> small amount of RAM. I'm not sure if it's possible to use cache-as-RAM >> in 64-bit mode... you'd need to read the CPU manufacturer's docs pretty >> carefully to find out. (I've never seen it done, but that doesn't >> necessarily mean it's impossible... SMM was never run in 64-bit mode in >> the past, and I was told it was impossible, but now it's done regularly.) >> >> A big "gotcha" for 64-bit mode is that it requires writable page tables, >> which requires generating the required tables in your cache-as-RAM in >> 32-bit mode (which uses several 4k pages of space, unless you're really >> clever about repurposing the unused table entries for other data) or >> implementing a TLB miss handler. If you can map all addresses with >> gigabyte-sized pages, and especially if you don't need to access the >> entire address space before MRC, the tables shouldn't take that much >> space. If you try to map a 2^46 address space with 4k pages, your >> tables will never fit in cache-as-RAM.... >> >> You may need to switch back to 32-bit mode to exit cache-as-RAM... not >> sure just what that dance would look like. It would probably take some >> experimentation. >> >> There may be other issues I haven't thought of. Good luck! >> -- >> >> Brian J. Johnson >> >> -------------------------------------------------------------------- >> >> "If you want your dreams to come true: Wake Up!" >> -- Jaime Roman's Radio >> >> > ---------------------------------------------------------------------------- > -- >> See everything from the browser to the database with AppDynamics >> Get end-to-end visibility with application monitoring from AppDynamics >> Isolate bottlenecks and diagnose root cause in seconds. >> Start your free trial of AppDynamics Pro today! >> > http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk >> _______________________________________________ >> edk2-devel mailing list >> edk2-devel@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/edk2-devel > ------------------------------------------------------------------------------ See everything from the browser to the database with AppDynamics Get end-to-end visibility with application monitoring from AppDynamics Isolate bottlenecks and diagnose root cause in seconds. Start your free trial of AppDynamics Pro today! http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk _______________________________________________ edk2-devel mailing list edk2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/edk2-devel
