On Tue, Apr 08, 2025 at 05:55:57AM -0700, Vishal Annapurve wrote:
On Tue, Apr 8, 2025 at 5:29 AM Greg Kroah-Hartman gregkh@linuxfoundation.org wrote:
6.13-stable review patch. If anyone has any objections, please let me know.
From: Vishal Annapurve vannapurve@google.com
commit 9f98a4f4e7216dbe366010b4cdcab6b220f229c4 upstream.
Direct HLT instruction execution causes #VEs for TDX VMs which is routed to hypervisor via TDCALL. If HLT is executed in STI-shadow, resulting #VE handler will enable interrupts before TDCALL is routed to hypervisor leading to missed wakeup events, as current TDX spec doesn't expose interruptibility state information to allow #VE handler to selectively enable interrupts.
Commit bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") prevented the idle routines from executing HLT instruction in STI-shadow. But it missed the paravirt routine which can be reached via this path as an example:
kvm_wait() => safe_halt() => raw_safe_halt() => arch_safe_halt() => irq.safe_halt() => pv_native_safe_halt()To reliably handle arch_safe_halt() for TDX VMs, introduce explicit dependency on CONFIG_PARAVIRT and override paravirt halt()/safe_halt() routines with TDX-safe versions that execute direct TDCALL and needed interrupt flag updates. Executing direct TDCALL brings in additional benefit of avoiding HLT related #VEs altogether.
As tested by Ryan Afranji:
"Tested with the specjbb2015 benchmark. It has heavy lock contention which leads to many halt calls. TDX VMs suffered a poor score before this patchset.
Verified the major performance improvement with this patchset applied."
Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") Signed-off-by: Vishal Annapurve vannapurve@google.com Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Tested-by: Ryan Afranji afranji@google.com Cc: Andy Lutomirski luto@kernel.org Cc: Brian Gerst brgerst@gmail.com Cc: Juergen Gross jgross@suse.com Cc: H. Peter Anvin hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250228014416.3925664-3-vannapurve@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
arch/x86/Kconfig | 1 + arch/x86/coco/tdx/tdx.c | 26 +++++++++++++++++++++++++- arch/x86/include/asm/tdx.h | 4 ++-- arch/x86/kernel/process.c | 2 +- 4 files changed, 29 insertions(+), 4 deletions(-)
Hi Greg,
This patch depends on commit 22cc5ca5de52 ("x86/paravirt: Move halt paravirt calls under CONFIG_PARAVIRT"). I will respond to the other thread with a patch for commit 22cc5ca5de52 after resolving conflicts.
That commit is already in this series, do I need to add it again? :)
thanks,
greg k-h