Messages in this thread Patch in this message | | | Date | Thu, 24 Feb 2022 15:12:20 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH v2 14/18] KVM: x86/mmu: avoid indirect call for get_cr3 |
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On Thu, Feb 24, 2022, Maxim Levitsky wrote: > Not sure though if that is worth it though. IMHO it would be better to > convert mmu callbacks (and nested ops callbacks, etc) to static calls.
nested_ops can utilize static_call(), mmu hooks cannot. static_call() patches the code, which means there cannot be multiple targets at any given time. The "static" part refers to the target not changing, generally for the lifetime of the kernel/module in question. Even with TDP that doesn't hold true due to nested virtualization.
We could selectively use INDIRECT_CALL_*() for some of the MMU calls, but given how few cases and targets we really care about, I prefer our homebrewed manual checks as theres less macro maze to navigate.
E.g. to convert the TDP fault case
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 1d0c1904d69a..940ec6a9d284 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -3,6 +3,8 @@ #define __KVM_X86_MMU_H
#include <linux/kvm_host.h> +#include <linux/indirect_call_wrapper.h> + #include "kvm_cache_regs.h" #include "cpuid.h"
@@ -169,7 +171,8 @@ struct kvm_page_fault { bool map_writable; };
-int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault); +INDIRECT_CALLABLE_DECLARE(int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, + struct kvm_page_fault *fault));
extern int nx_huge_pages; static inline bool is_nx_huge_page_enabled(void) @@ -196,11 +199,9 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, .req_level = PG_LEVEL_4K, .goal_level = PG_LEVEL_4K, }; -#ifdef CONFIG_RETPOLINE - if (fault.is_tdp) - return kvm_tdp_page_fault(vcpu, &fault); -#endif - return vcpu->arch.mmu->page_fault(vcpu, &fault); + struct kvm_mmu *mmu = vcpu->arch.mmu; + + return INDIRECT_CALL_1(mmu->page_fault, kvm_tdp_page_fault, vcpu, &fault); }
/* diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index c1deaec795c2..a3ad1bc58859 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4055,7 +4055,8 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code, } EXPORT_SYMBOL_GPL(kvm_handle_page_fault);
-int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) +INDIRECT_CALLABLE_SCOPE int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, + struct kvm_page_fault *fault) { while (fault->max_level > PG_LEVEL_4K) { int page_num = KVM_PAGES_PER_HPAGE(fault->max_level);
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