KVM: x86: Expand build-time assertion on reverse CPUID usage (a7c48c3f) · Commits · 戴 / test

arch/x86/kvm/cpuid.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -281,8 +281,9 @@ out:
		return r;
		}

		static void cpuid_mask(u32 *word, int wordnum)
		static __always_inline void cpuid_mask(u32 *word, int wordnum)
		{
		reverse_cpuid_check(wordnum);
		*word &= boot_cpu_data.x86_capability[wordnum];
		}

arch/x86/kvm/cpuid.h

+28 −5

Original line number	Diff line number	Diff line
		@@ -56,18 +56,41 @@ static const struct cpuid_reg reverse_cpuid[] = {
		[CPUID_7_1_EAX] = { 7, 1, CPUID_EAX},
		};

		static inline u32 bit(int bitno)
		/*
		* Reverse CPUID and its derivatives can only be used for hardware-defined
		* feature words, i.e. words whose bits directly correspond to a CPUID leaf.
		* Retrieving a feature bit or masking guest CPUID from a Linux-defined word
		* is nonsensical as the bit number/mask is an arbitrary software-defined value
		* and can't be used by KVM to query/control guest capabilities. And obviously
		* the leaf being queried must have an entry in the lookup table.
		*/
		static __always_inline void reverse_cpuid_check(unsigned x86_leaf)
		{
		return BIT(bitno & 31);
		BUILD_BUG_ON(x86_leaf == CPUID_LNX_1);
		BUILD_BUG_ON(x86_leaf == CPUID_LNX_2);
		BUILD_BUG_ON(x86_leaf == CPUID_LNX_3);
		BUILD_BUG_ON(x86_leaf == CPUID_LNX_4);
		BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
		BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
		}

		/*
		* Retrieve the bit mask from an X86_FEATURE_* definition. Features contain
		* the hardware defined bit number (stored in bits 4:0) and a software defined
		* "word" (stored in bits 31:5). The word is used to index into arrays of
		* bit masks that hold the per-cpu feature capabilities, e.g. this_cpu_has().
		*/
		static __always_inline u32 bit(int x86_feature)
		{
		reverse_cpuid_check(x86_feature / 32);
		return 1 << (x86_feature & 31);
		}

		static __always_inline struct cpuid_reg x86_feature_cpuid(unsigned x86_feature)
		{
		unsigned x86_leaf = x86_feature / 32;

		BUILD_BUG_ON(x86_leaf >= ARRAY_SIZE(reverse_cpuid));
		BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);

		reverse_cpuid_check(x86_leaf);
		return reverse_cpuid[x86_leaf];
		}

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