From: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com
CONFIG_PARAVIRT_XXL is mainly defined/used by XEN PV guests. For other VM guest types, features supported under CONFIG_PARAVIRT are self sufficient. CONFIG_PARAVIRT mainly provides support for TLB flush operations and time related operations.
For TDX guest as well, paravirt calls under CONFIG_PARVIRT meets most of its requirement except the need of HLT and SAFE_HLT paravirt calls, which is currently defined under CONFIG_PARAVIRT_XXL.
Since enabling CONFIG_PARAVIRT_XXL is too bloated for TDX guest like platforms, move HLT and SAFE_HLT paravirt calls under CONFIG_PARAVIRT.
Moving HLT and SAFE_HLT paravirt calls are not fatal and should not break any functionality for current users of CONFIG_PARAVIRT.
Cc: stable@vger.kernel.org Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") Co-developed-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com Signed-off-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reviewed-by: Andi Kleen ak@linux.intel.com Reviewed-by: Tony Luck tony.luck@intel.com Signed-off-by: Vishal Annapurve vannapurve@google.com --- arch/x86/include/asm/irqflags.h | 40 +++++++++++++++------------ arch/x86/include/asm/paravirt.h | 20 +++++++------- arch/x86/include/asm/paravirt_types.h | 3 +- arch/x86/kernel/paravirt.c | 14 ++++++---- 4 files changed, 41 insertions(+), 36 deletions(-)
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index cf7fc2b8e3ce..1c2db11a2c3c 100644 --- a/arch/x86/include/asm/irqflags.h +++ b/arch/x86/include/asm/irqflags.h @@ -76,6 +76,28 @@ static __always_inline void native_local_irq_restore(unsigned long flags)
#endif
+#ifndef CONFIG_PARAVIRT +#ifndef __ASSEMBLY__ +/* + * Used in the idle loop; sti takes one instruction cycle + * to complete: + */ +static __always_inline void arch_safe_halt(void) +{ + native_safe_halt(); +} + +/* + * Used when interrupts are already enabled or to + * shutdown the processor: + */ +static __always_inline void halt(void) +{ + native_halt(); +} +#endif /* __ASSEMBLY__ */ +#endif /* CONFIG_PARAVIRT */ + #ifdef CONFIG_PARAVIRT_XXL #include <asm/paravirt.h> #else @@ -97,24 +119,6 @@ static __always_inline void arch_local_irq_enable(void) native_irq_enable(); }
-/* - * Used in the idle loop; sti takes one instruction cycle - * to complete: - */ -static __always_inline void arch_safe_halt(void) -{ - native_safe_halt(); -} - -/* - * Used when interrupts are already enabled or to - * shutdown the processor: - */ -static __always_inline void halt(void) -{ - native_halt(); -} - /* * For spinlocks, etc: */ diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h index 041aff51eb50..29e7331a0c98 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -107,6 +107,16 @@ static inline void notify_page_enc_status_changed(unsigned long pfn, PVOP_VCALL3(mmu.notify_page_enc_status_changed, pfn, npages, enc); }
+static __always_inline void arch_safe_halt(void) +{ + PVOP_VCALL0(irq.safe_halt); +} + +static inline void halt(void) +{ + PVOP_VCALL0(irq.halt); +} + #ifdef CONFIG_PARAVIRT_XXL static inline void load_sp0(unsigned long sp0) { @@ -170,16 +180,6 @@ static inline void __write_cr4(unsigned long x) PVOP_VCALL1(cpu.write_cr4, x); }
-static __always_inline void arch_safe_halt(void) -{ - PVOP_VCALL0(irq.safe_halt); -} - -static inline void halt(void) -{ - PVOP_VCALL0(irq.halt); -} - static inline u64 paravirt_read_msr(unsigned msr) { return PVOP_CALL1(u64, cpu.read_msr, msr); diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index fea56b04f436..abccfccc2e3f 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -120,10 +120,9 @@ struct pv_irq_ops { struct paravirt_callee_save save_fl; struct paravirt_callee_save irq_disable; struct paravirt_callee_save irq_enable; - +#endif void (*safe_halt)(void); void (*halt)(void); -#endif } __no_randomize_layout;
struct pv_mmu_ops { diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index 1ccaa3397a67..c5bb980b8a67 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -110,6 +110,11 @@ int paravirt_disable_iospace(void) return request_resource(&ioport_resource, &reserve_ioports); }
+static noinstr void pv_native_safe_halt(void) +{ + native_safe_halt(); +} + #ifdef CONFIG_PARAVIRT_XXL static noinstr void pv_native_write_cr2(unsigned long val) { @@ -125,11 +130,6 @@ static noinstr void pv_native_set_debugreg(int regno, unsigned long val) { native_set_debugreg(regno, val); } - -static noinstr void pv_native_safe_halt(void) -{ - native_safe_halt(); -} #endif
struct pv_info pv_info = { @@ -186,9 +186,11 @@ struct paravirt_patch_template pv_ops = { .irq.save_fl = __PV_IS_CALLEE_SAVE(pv_native_save_fl), .irq.irq_disable = __PV_IS_CALLEE_SAVE(pv_native_irq_disable), .irq.irq_enable = __PV_IS_CALLEE_SAVE(pv_native_irq_enable), +#endif /* CONFIG_PARAVIRT_XXL */ + + /* Irq HLT ops. */ .irq.safe_halt = pv_native_safe_halt, .irq.halt = native_halt, -#endif /* CONFIG_PARAVIRT_XXL */
/* Mmu ops. */ .mmu.flush_tlb_user = native_flush_tlb_local,
On 2/20/25 13:16, Vishal Annapurve wrote:
Since enabling CONFIG_PARAVIRT_XXL is too bloated for TDX guest like platforms, move HLT and SAFE_HLT paravirt calls under CONFIG_PARAVIRT.
I guess it's just one patch, but doesn't this expose CONFIG_PARAVIRT=y users to what _was_ specific to CONFIG_PARAVIRT_XXL=y? According to the changelog, TDX users shouldn't have to use use PARAVIRT_XXL, so PARAVIRT=y and PARAVIRT_XXL=n must be an *IMPORTANT* configuration for TDX users.
Before this patch, those users would have no way to hit the unsafe-for-TDX pv_native_safe_halt(). After this patch, they will hit it.
So, there are two possibilities:
1. This patch breaks bisection for an important TDX configuration 2. This patch's conjecture that PARAVIRT_XXL=n is important for TDX is wrong and it is not necessary in the first place.
What am I missing?
On Thu, Feb 20, 2025 at 1:47 PM Dave Hansen dave.hansen@intel.com wrote:
On 2/20/25 13:16, Vishal Annapurve wrote:
Since enabling CONFIG_PARAVIRT_XXL is too bloated for TDX guest like platforms, move HLT and SAFE_HLT paravirt calls under CONFIG_PARAVIRT.
I guess it's just one patch, but doesn't this expose CONFIG_PARAVIRT=y users to what _was_ specific to CONFIG_PARAVIRT_XXL=y? According to the changelog, TDX users shouldn't have to use use PARAVIRT_XXL, so PARAVIRT=y and PARAVIRT_XXL=n must be an *IMPORTANT* configuration for TDX users.
Before this patch, those users would have no way to hit the unsafe-for-TDX pv_native_safe_halt(). After this patch, they will hit it.
Before this patch, those users had access to arch_safe_halt() -> native_safe_halt() path. With this patch, such users can execute arch_safe_halt -> pv_native_safe_halt() -> native_safe_halt(), so this patch doesn't cause any additional regression.
So, there are two possibilities:
- This patch breaks bisection for an important TDX configuration
- This patch's conjecture that PARAVIRT_XXL=n is important for TDX is wrong and it is not necessary in the first place.
What am I missing?
On Thu, Feb 20, 2025 at 09:16:25PM +0000, Vishal Annapurve wrote:
From: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com
CONFIG_PARAVIRT_XXL is mainly defined/used by XEN PV guests. For other VM guest types, features supported under CONFIG_PARAVIRT are self sufficient. CONFIG_PARAVIRT mainly provides support for TLB flush operations and time related operations.
For TDX guest as well, paravirt calls under CONFIG_PARVIRT meets most of its requirement except the need of HLT and SAFE_HLT paravirt calls, which is currently defined under CONFIG_PARAVIRT_XXL.
Since enabling CONFIG_PARAVIRT_XXL is too bloated for TDX guest like platforms, move HLT and SAFE_HLT paravirt calls under CONFIG_PARAVIRT.
Could you use the bloat-o-meter to give an idea of the savings?
Also .. aren't most distros building with Xen support so they will always have the full paravirt support?
Moving HLT and SAFE_HLT paravirt calls are not fatal and should not break any functionality for current users of CONFIG_PARAVIRT.
Cc: stable@vger.kernel.org Fixes: bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests") Co-developed-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com Signed-off-by: Kuppuswamy Sathyanarayanan sathyanarayanan.kuppuswamy@linux.intel.com Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reviewed-by: Andi Kleen ak@linux.intel.com Reviewed-by: Tony Luck tony.luck@intel.com Signed-off-by: Vishal Annapurve vannapurve@google.com
arch/x86/include/asm/irqflags.h | 40 +++++++++++++++------------ arch/x86/include/asm/paravirt.h | 20 +++++++------- arch/x86/include/asm/paravirt_types.h | 3 +- arch/x86/kernel/paravirt.c | 14 ++++++---- 4 files changed, 41 insertions(+), 36 deletions(-)
diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h index cf7fc2b8e3ce..1c2db11a2c3c 100644 --- a/arch/x86/include/asm/irqflags.h +++ b/arch/x86/include/asm/irqflags.h @@ -76,6 +76,28 @@ static __always_inline void native_local_irq_restore(unsigned long flags) #endif +#ifndef CONFIG_PARAVIRT +#ifndef __ASSEMBLY__ +/*
- Used in the idle loop; sti takes one instruction cycle
- to complete:
- */
+static __always_inline void arch_safe_halt(void) +{
- native_safe_halt();
+}
+/*
- Used when interrupts are already enabled or to
- shutdown the processor:
- */
+static __always_inline void halt(void) +{
- native_halt();
+} +#endif /* __ASSEMBLY__ */ +#endif /* CONFIG_PARAVIRT */
#ifdef CONFIG_PARAVIRT_XXL #include <asm/paravirt.h> #else @@ -97,24 +119,6 @@ static __always_inline void arch_local_irq_enable(void) native_irq_enable(); } -/*
- Used in the idle loop; sti takes one instruction cycle
- to complete:
- */
-static __always_inline void arch_safe_halt(void) -{
- native_safe_halt();
-}
-/*
- Used when interrupts are already enabled or to
- shutdown the processor:
- */
-static __always_inline void halt(void) -{
- native_halt();
-}
/*
- For spinlocks, etc:
*/ diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h index 041aff51eb50..29e7331a0c98 100644 --- a/arch/x86/include/asm/paravirt.h +++ b/arch/x86/include/asm/paravirt.h @@ -107,6 +107,16 @@ static inline void notify_page_enc_status_changed(unsigned long pfn, PVOP_VCALL3(mmu.notify_page_enc_status_changed, pfn, npages, enc); } +static __always_inline void arch_safe_halt(void) +{
- PVOP_VCALL0(irq.safe_halt);
+}
+static inline void halt(void) +{
- PVOP_VCALL0(irq.halt);
+}
#ifdef CONFIG_PARAVIRT_XXL static inline void load_sp0(unsigned long sp0) { @@ -170,16 +180,6 @@ static inline void __write_cr4(unsigned long x) PVOP_VCALL1(cpu.write_cr4, x); } -static __always_inline void arch_safe_halt(void) -{
- PVOP_VCALL0(irq.safe_halt);
-}
-static inline void halt(void) -{
- PVOP_VCALL0(irq.halt);
-}
static inline u64 paravirt_read_msr(unsigned msr) { return PVOP_CALL1(u64, cpu.read_msr, msr); diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h index fea56b04f436..abccfccc2e3f 100644 --- a/arch/x86/include/asm/paravirt_types.h +++ b/arch/x86/include/asm/paravirt_types.h @@ -120,10 +120,9 @@ struct pv_irq_ops { struct paravirt_callee_save save_fl; struct paravirt_callee_save irq_disable; struct paravirt_callee_save irq_enable;
+#endif void (*safe_halt)(void); void (*halt)(void); -#endif } __no_randomize_layout; struct pv_mmu_ops { diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c index 1ccaa3397a67..c5bb980b8a67 100644 --- a/arch/x86/kernel/paravirt.c +++ b/arch/x86/kernel/paravirt.c @@ -110,6 +110,11 @@ int paravirt_disable_iospace(void) return request_resource(&ioport_resource, &reserve_ioports); } +static noinstr void pv_native_safe_halt(void) +{
- native_safe_halt();
+}
#ifdef CONFIG_PARAVIRT_XXL static noinstr void pv_native_write_cr2(unsigned long val) { @@ -125,11 +130,6 @@ static noinstr void pv_native_set_debugreg(int regno, unsigned long val) { native_set_debugreg(regno, val); }
-static noinstr void pv_native_safe_halt(void) -{
- native_safe_halt();
-} #endif struct pv_info pv_info = { @@ -186,9 +186,11 @@ struct paravirt_patch_template pv_ops = { .irq.save_fl = __PV_IS_CALLEE_SAVE(pv_native_save_fl), .irq.irq_disable = __PV_IS_CALLEE_SAVE(pv_native_irq_disable), .irq.irq_enable = __PV_IS_CALLEE_SAVE(pv_native_irq_enable), +#endif /* CONFIG_PARAVIRT_XXL */
- /* Irq HLT ops. */ .irq.safe_halt = pv_native_safe_halt, .irq.halt = native_halt,
-#endif /* CONFIG_PARAVIRT_XXL */ /* Mmu ops. */ .mmu.flush_tlb_user = native_flush_tlb_local, -- 2.48.1.601.g30ceb7b040-goog
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