Commit 4e629211 authored by Juergen Gross's avatar Juergen Gross Committed by Borislav Petkov
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x86/paravirt: Add new features for paravirt patching 



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 alternatives patching.

Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210311142319.4723-9-jgross@suse.com
parent 2fe2a2c7

arch/x86/include/asm/cpufeatures.h

+2 −0
Original line number Diff line number Diff line
@@ -236,6 +236,8 @@ 
#define X86_FEATURE_EPT_AD		( 8*32+17) /* Intel Extended Page Table access-dirty bit */

#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_PVUNLOCK		( 8*32+20) /* "" PV unlock function */

#define X86_FEATURE_VCPUPREEMPT		( 8*32+21) /* "" 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*/

arch/x86/include/asm/paravirt.h

+10 −0
Original line number Diff line number Diff line
@@ -45,6 +45,10 @@ static inline u64 paravirt_steal_clock(int cpu) 
	return static_call(pv_steal_clock)(cpu);

}



#ifdef CONFIG_PARAVIRT_SPINLOCKS

void __init paravirt_set_cap(void);

#endif



/* The paravirtualized I/O functions */

static inline void slow_down_io(void)

{
@@ -809,5 +813,11 @@ static inline void paravirt_arch_exit_mmap(struct mm_struct *mm) 
{

}

#endif



#ifndef CONFIG_PARAVIRT_SPINLOCKS

static inline void paravirt_set_cap(void)

{

}

#endif

#endif /* __ASSEMBLY__ */

#endif /* _ASM_X86_PARAVIRT_H */

arch/x86/kernel/alternative.c

+28 −2
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ 
#include <asm/insn.h>

#include <asm/io.h>

#include <asm/fixmap.h>

#include <asm/paravirt.h>



int __read_mostly alternatives_patched;
@@ -733,6 +734,33 @@ void __init alternative_instructions(void) 
	 * patching.

	 */



	/*

	 * Paravirt patching and alternative patching can be combined to

	 * replace a function call with a short direct code sequence (e.g.

	 * by setting a constant return value instead of doing that in an

	 * external function).

	 * In order to make this work the following sequence is required:

	 * 1. set (artificial) features depending on used paravirt

	 *    functions which can later influence alternative patching

	 * 2. apply paravirt patching (generally replacing an indirect

	 *    function call with a direct one)

	 * 3. apply alternative patching (e.g. replacing a direct function

	 *    call with a custom code sequence)

	 * Doing paravirt patching after alternative patching would clobber

	 * the optimization of the custom code with a function call again.

	 */

	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
@@ -751,8 +779,6 @@ void __init alternative_instructions(void) 
	}

#endif



	apply_paravirt(__parainstructions, __parainstructions_end);



	restart_nmi();

	alternatives_patched = 1;

}

arch/x86/kernel/paravirt-spinlocks.c

+9 −0
Original line number Diff line number Diff line
@@ -32,3 +32,12 @@ bool pv_is_native_vcpu_is_preempted(void) 
	return pv_ops.lock.vcpu_is_preempted.func ==

		__raw_callee_save___native_vcpu_is_preempted;

}



void __init paravirt_set_cap(void)

{

	if (!pv_is_native_spin_unlock())

		setup_force_cpu_cap(X86_FEATURE_PVUNLOCK);



	if (!pv_is_native_vcpu_is_preempted())

		setup_force_cpu_cap(X86_FEATURE_VCPUPREEMPT);

}