[PATCH v2 07/12] x86: add new features for paravirt patching

From: Juergen Gross
Date: Fri Nov 20 2020 - 06:47:04 EST


For being able to switch paravirt patching from special cased custom
code sequences to ALTERNATIVE handling some X86_FEATURE_* are needed
as new features. This enables to have the standard indirect pv call
as the default code and to patch that with the non-Xen custom code
sequence via ALTERNATIVE patching later.

Make sure paravirt patching is performed before alternative patching.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
arch/x86/include/asm/cpufeatures.h | 3 +++
arch/x86/kernel/alternative.c | 28 ++++++++++++++++++++++++++--
2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index dad350d42ecf..ffa23c655412 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -237,6 +237,9 @@
#define X86_FEATURE_VMCALL ( 8*32+18) /* "" Hypervisor supports the VMCALL instruction */
#define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
#define X86_FEATURE_SEV_ES ( 8*32+20) /* AMD Secure Encrypted Virtualization - Encrypted State */
+#define X86_FEATURE_NOT_XENPV ( 8*32+21) /* "" Inverse of X86_FEATURE_XENPV */
+#define X86_FEATURE_NO_PVUNLOCK ( 8*32+22) /* "" No PV unlock function */
+#define X86_FEATURE_NO_VCPUPREEMPT ( 8*32+23) /* "" No PV vcpu_is_preempted function */

/* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
#define X86_FEATURE_FSGSBASE ( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 2400ad62f330..f8f9700719cf 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -593,6 +593,18 @@ int alternatives_text_reserved(void *start, void *end)
#endif /* CONFIG_SMP */

#ifdef CONFIG_PARAVIRT
+static void __init paravirt_set_cap(void)
+{
+ if (!boot_cpu_has(X86_FEATURE_XENPV))
+ setup_force_cpu_cap(X86_FEATURE_NOT_XENPV);
+
+ if (pv_is_native_spin_unlock())
+ setup_force_cpu_cap(X86_FEATURE_NO_PVUNLOCK);
+
+ if (pv_is_native_vcpu_is_preempted())
+ setup_force_cpu_cap(X86_FEATURE_NO_VCPUPREEMPT);
+}
+
void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
struct paravirt_patch_site *end)
{
@@ -616,6 +628,8 @@ void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
}
extern struct paravirt_patch_site __start_parainstructions[],
__stop_parainstructions[];
+#else
+static void __init paravirt_set_cap(void) { }
#endif /* CONFIG_PARAVIRT */

/*
@@ -723,6 +737,18 @@ void __init alternative_instructions(void)
* patching.
*/

+ paravirt_set_cap();
+
+ /*
+ * First patch paravirt functions, such that we overwrite the indirect
+ * call with the direct call.
+ */
+ apply_paravirt(__parainstructions, __parainstructions_end);
+
+ /*
+ * Then patch alternatives, such that those paravirt calls that are in
+ * alternatives can be overwritten by their immediate fragments.
+ */
apply_alternatives(__alt_instructions, __alt_instructions_end);

#ifdef CONFIG_SMP
@@ -741,8 +767,6 @@ void __init alternative_instructions(void)
}
#endif

- apply_paravirt(__parainstructions, __parainstructions_end);
-
restart_nmi();
alternatives_patched = 1;
}
--
2.26.2