Messages in this thread | | | Date | Fri, 4 Feb 2022 03:27:19 -0800 | Subject | Re: [PATCHv2 16/29] x86/boot: Add a trampoline for booting APs via firmware handoff | From | "Kuppuswamy, Sathyanarayanan" <> |
| |
On 2/2/2022 3:27 AM, Borislav Petkov wrote: > On Mon, Jan 24, 2022 at 06:02:02PM +0300, Kirill A. Shutemov wrote: >> From: Sean Christopherson <sean.j.christopherson@intel.com> >> >> Historically, x86 platforms have booted secondary processors (APs) >> using INIT followed by the start up IPI (SIPI) messages. In regular >> VMs, this boot sequence is supported by the VMM emulation. But such a >> wakeup model is fatal for secure VMs like TDX in which VMM is an >> untrusted entity. To address this issue, a new wakeup model was added >> in ACPI v6.4, in which firmware (like TDX virtual BIOS) will help boot >> the APs. More details about this wakeup model can be found in ACPI >> specification v6.4, the section titled "Multiprocessor Wakeup Structure". >> >> Since the existing trampoline code requires processors to boot in real >> mode with 16-bit addressing, it will not work for this wakeup model >> (because it boots the AP in 64-bit mode). To handle it, extend the >> trampoline code to support 64-bit mode firmware handoff. Also, extend >> IDT and GDT pointers to support 64-bit mode hand off. >> >> There is no TDX-specific detection for this new boot method. The kernel >> will rely on it as the sole boot method whenever the new ACPI structure >> is present. >> >> The ACPI table parser for the MADT multiprocessor wake up structure and >> the wakeup method that uses this structure will be added by the following >> patch in this series. >> >> Reported-by: Kai Huang <kai.huang@intel.com> > I wonder what that Reported-by tag means here for this is a feature > patch, not a bug fix or so...
I think it was added when Sean created the original patch. I don't have the full history.
Sean, since this is not a bug fix, shall we remove the Reported-by tag?
> >> diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h >> index 331474b150f1..fd6f6e5b755a 100644 >> --- a/arch/x86/include/asm/realmode.h >> +++ b/arch/x86/include/asm/realmode.h >> @@ -25,6 +25,7 @@ struct real_mode_header { >> u32 sev_es_trampoline_start; >> #endif >> #ifdef CONFIG_X86_64 >> + u32 trampoline_start64; >> u32 trampoline_pgd; >> #endif > Hmm, so there's trampoline_start, sev_es_trampoline_start and > trampoline_start64. If those are mutually exclusive, can we merge them > all into a single trampoline_start?
trampoline_start and sev_es_trampoline_start are not mutually exclusive. Both are used in arch/x86/kernel/sev.c.
arch/x86/kernel/sev.c:560: startup_ip = (u16)(rmh->sev_es_trampoline_start - arch/x86/kernel/sev.c:561: rmh->trampoline_start);
But trampoline_start64 can be removed and replaced with trampoline_start. But using _*64 suffix makes it clear that is used for 64 bit(CONFIG_X86_64).
Adding it for clarity seems to be fine to me. But if you would prefer single variable, we can remove it. Please let me know.
> -- Sathyanarayanan Kuppuswamy Linux Kernel Developer
| |