Messages in this thread | | | Date | Fri, 6 Oct 2023 17:15:37 -0500 | Subject | Re: [PATCH 10/13] x86/tdx: Convert shared memory back to private on kexec | From | "Kalra, Ashish" <> |
| |
On 10/6/2023 10:11 AM, Kirill A. Shutemov wrote: > On Fri, Oct 06, 2023 at 07:58:03AM -0700, Sean Christopherson wrote: >> On Thu, Oct 05, 2023, Kirill A. Shutemov wrote: >>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >>> index 7368d254d01f..b5acf9fb4c70 100644 >>> --- a/arch/x86/Kconfig >>> +++ b/arch/x86/Kconfig >>> @@ -884,6 +884,7 @@ config INTEL_TDX_GUEST >>> select X86_MEM_ENCRYPT >>> select X86_MCE >>> select UNACCEPTED_MEMORY >>> + select EMERGENCY_VIRT_CALLBACK >>> help >>> Support running as a guest under Intel TDX. Without this support, >>> the guest kernel can not boot or run under TDX. >> >> ... >> >>> void __init tdx_early_init(void) >>> { >>> struct tdx_module_args args = { >>> @@ -882,6 +1007,14 @@ void __init tdx_early_init(void) >>> */ >>> x86_cpuinit.parallel_bringup = false; >>> >>> + machine_ops.shutdown = tdx_shutdown; >>> + >>> + /* >>> + * KVM overrides machine_ops.crash_shutdown, use emergency >> >> This is going to be super confusing. KVM utilizes the emergency virt callback. >> The KVM paravirt guest code uses .crash_shutdown(). People that are passingly >> familiar with virt and know what KVM is, but don't already know the difference >> between the two are going to be all kinds of confused. >> >> I also feel like you're playing with fire, e.g. what's to stop the hypervisor >> specific paravirt guest support from using .shutdown() in the future? >> >> And the callback is invoked for far more than just kexec(). I don't see how the >> host can emulate a reboot without destroying and rebuilding the VM, e.g. it can't >> stuff register state to emulate INIT or RESET. Unless I'm missing something, >> converting shared memory back to private for a shutdown or reboot is undesirable >> as adds one more thing that can go wrong and prevent the system from cleanly >> shutting down ASAP (for some definitions of "cleanly"). > > Okay, fair enough. I will look for better way to hookup into kexec > process. That was the best fit I found so far, but yes it is not ideal. > >> Lastly, doesn't SEV need similar behavior? This seems like core functionality >> for any guest with cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT). Why not make the >> "unshare on kexec" code common and gate it with CC_ATTR_GUEST_MEM_ENCRYPT? > > I don't know SEV specifics. I am open to collaboration on this. > > Tom, Ashish, let me know if you need this in generic code. I can arrange > that. >
Yes, some kind of a generic interface like unshare_on_kexec() gated with CC_ATTR_GUEST_MEM_ENCRYPT is needed, we can then add SNP specific kexec functionality as part of this.
Thanks, Ashish
| |