On Thu, Jan 30, 2025 at 09:24:37AM -0800, Vishal Annapurve wrote: > On Thu, Jan 30, 2025 at 1:28 AM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > > > On Wed, Jan 29, 2025 at 11:25:25PM +0000, Vishal Annapurve wrote: > > > Direct HLT instruction execution causes #VEs for TDX VMs which is routed > > > to hypervisor via tdvmcall. This process renders HLT instruction > > > execution inatomic, so any preceding instructions like STI/MOV SS will > > > end up enabling interrupts before the HLT instruction is routed to the > > > hypervisor. This creates scenarios where interrupts could land during > > > HLT instruction emulation without aborting halt operation leading to > > > idefinite halt wait times. > > > > > > Commit bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") already > > > upgraded x86_idle() to invoke tdvmcall to avoid such scenarios, but > > > it didn't cover pv_native_safe_halt() which can be invoked using > > > raw_safe_halt() from call sites like acpi_safe_halt(). > > > > > > raw_safe_halt() also returns with interrupts enabled so upgrade > > > tdx_safe_halt() to enable interrupts by default and ensure that paravirt > > > safe_halt() executions invoke tdx_safe_halt(). Earlier x86_idle() is now > > > handled via tdx_idle() which simply invokes tdvmcall while preserving > > > irq state. > > > > > > To avoid future call sites which cause HLT instruction emulation with > > > irqs enabled, add a warn and fail the HLT instruction emulation. > > > > > > Cc: stable@xxxxxxxxxxxxxxx > > > Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") > > > Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx> > > > --- > > > Changes since V1: > > > 1) Addressed comments from Dave H > > > - Comment regarding adding a check for TDX VMs in halt path is not > > > resolved in v2, would like feedback around better place to do so, > > > maybe in pv_native_safe_halt (?). > > > 2) Added a new version of tdx_safe_halt() that will enable interrupts. > > > 3) Previous tdx_safe_halt() implementation is moved to newly introduced > > > tdx_idle(). > > > > > > V1: https://lore.kernel.org/lkml/Z5l6L3Hen9_Y3SGC@xxxxxxxxxx/T/ > > > > > > arch/x86/coco/tdx/tdx.c | 23 ++++++++++++++++++++++- > > > arch/x86/include/asm/tdx.h | 2 +- > > > arch/x86/kernel/process.c | 2 +- > > > 3 files changed, 24 insertions(+), 3 deletions(-) > > > > > > diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c > > > index 0d9b090b4880..cc2a637dca15 100644 > > > --- a/arch/x86/coco/tdx/tdx.c > > > +++ b/arch/x86/coco/tdx/tdx.c > > > @@ -14,6 +14,7 @@ > > > #include <asm/ia32.h> > > > #include <asm/insn.h> > > > #include <asm/insn-eval.h> > > > +#include <asm/paravirt_types.h> > > > #include <asm/pgtable.h> > > > #include <asm/set_memory.h> > > > #include <asm/traps.h> > > > @@ -380,13 +381,18 @@ static int handle_halt(struct ve_info *ve) > > > { > > > const bool irq_disabled = irqs_disabled(); > > > > > > + if (!irq_disabled) { > > > + WARN_ONCE(1, "HLT instruction emulation unsafe with irqs enabled\n"); > > > + return -EIO; > > > + } > > > + > > > > I think it is worth to putting this into a separate patch and not > > backport. The rest of the patch is bugfix and this doesn't belong. > > > > Otherwise, looks good to me: > > > > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>@linux.intel.com> > > > > -- > > Kiryl Shutsemau / Kirill A. Shutemov > > Thanks Kirill for the review. > > Thinking more about this fix, now I am wondering why the efforts [1] > to move halt/safe_halt under CONFIG_PARAVIRT were abandoned. Currently > proposed fix is incomplete as it would not handle scenarios where > CONFIG_PARAVIRT_XXL is disabled. I am tilting towards reviving [1] and > requiring CONFIG_PARAVIRT for TDX VMs. WDYT? > > [1] https://lore.kernel.org/lkml/20210517235008.257241-1-sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx/ Many people dislike paravirt callbacks. We tried to avoid relying on them for core TDX enabling. Can you explain the issue you see with CONFIG_PARAVIRT_XXL being disabled? I don't think I follow. -- Kiryl Shutsemau / Kirill A. Shutemov