Re: [PATCH v7 0/3] x86/tdx: Fix HLT logic execution for TDX VMs

[Vishal Annapurve]

On Thu, Feb 27, 2025 at 5:44 PM Vishal Annapurve <vannapurve@xxxxxxxxxx> wrote:
>
> Direct HLT instruction execution causes #VEs for TDX VMs which is routed
> to hypervisor via TDCALL. safe_halt() routines execute HLT in STI-shadow
> so IRQs need to remain disabled until the TDCALL to ensure that pending
> IRQs are correctly treated as wake events. As per current TDX spec, HLT
> #VE handler doesn't have access to interruptibility state to selectively
> enable interrupts, it ends up enabling interrupts during #VE handling
> before the TDCALL is executed.
>
> Commit bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests")
> effectively solved this issue for idle routines by defining TDX specific
> idle routine which directly invokes TDCALL while keeping interrupts
> disabled, but missed handling arch_safe_halt(). This series intends to fix
> arch_safe_halt() execution for TDX VMs.
>
> Changes introduced by the series include:
> - Move *halt() variants outside CONFIG_PARAVIRT_XXL and under
>   CONFIG_PARAVIRT [1].
> - Add explicit dependency on CONFIG_PARAVIRT for TDX VMs.
> - Route "sti; hlt" sequences via tdx_safe_halt() for reliability.
> - Route "hlt" sequences via tdx_halt() to avoid unnecessary #VEs.
> - Warn and fail emulation if HLT #VE emulation executes with interrupts
>   enabled.
>
> Changes since v6:
> 1) Addressed Kirills's comments.
> 2) Fixed a build failure.
>
> v6: https://lore.kernel.org/lkml/20250225004704.603652-1-vannapurve@xxxxxxxxxx/
>
> Kirill A. Shutemov (1):
>   x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT
>
> Vishal Annapurve (2):
>   x86/tdx: Fix arch_safe_halt() execution for TDX VMs
>   x86/tdx: Emit warning if IRQs are enabled during HLT #VE handling
>
>  arch/x86/Kconfig                      |  1 +
>  arch/x86/coco/tdx/tdx.c               | 34 ++++++++++++++++++++++-
>  arch/x86/include/asm/irqflags.h       | 40 +++++++++++++++------------
>  arch/x86/include/asm/paravirt.h       | 20 +++++++-------
>  arch/x86/include/asm/paravirt_types.h |  3 +-
>  arch/x86/include/asm/tdx.h            |  4 +--
>  arch/x86/kernel/paravirt.c            | 14 ++++++----
>  arch/x86/kernel/process.c             |  2 +-
>  8 files changed, 78 insertions(+), 40 deletions(-)
>
> --
> 2.48.1.711.g2feabab25a-goog
>

Just a ping for review of this series if anything more needs to be discussed.