kvm: vmx: Reduce size of vmcs_field_to_offset_table

Web:        https://git.kernel.org/torvalds/c/58e9ffae5efd3ee9b655ee36702f02c36d51ead9
Commit:     58e9ffae5efd3ee9b655ee36702f02c36d51ead9
Parent:     d37f4267a79f7d423103cb9fdd67a4a3a8194335
Refname:    refs/heads/master
Author:     Jim Mattson <[email protected]>
AuthorDate: Fri Dec 22 12:13:13 2017 -0800
Committer:  Radim Krčmář <[email protected]>
CommitDate: Tue Jan 16 16:50:03 2018 +0100

    kvm: vmx: Reduce size of vmcs_field_to_offset_table
    
    The vmcs_field_to_offset_table was a rather sparse table of short
    integers with a maximum index of 0x6c16, amounting to 55342 bytes. Now
    that we are considering support for multiple VMCS12 formats, it would
    be unfortunate to replicate that large, sparse table. Rotating the
    field encoding (as a 16-bit integer) left by 6 reduces that table to
    5926 bytes.
    
    Suggested-by: Paolo Bonzini <[email protected]>
    Signed-off-by: Jim Mattson <[email protected]>
    Signed-off-by: Paolo Bonzini <[email protected]>
    Signed-off-by: Radim Krčmář <[email protected]>
---
 arch/x86/kvm/vmx.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f1d41dd3744c..d49bb747ebea 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -686,10 +686,12 @@ static struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
 	return &(to_vmx(vcpu)->pi_desc);
 }
 
+#define ROL16(val, n) ((u16)(((u16)(val) << (n)) | ((u16)(val) >> (16 - (n)))))
 #define VMCS12_OFFSET(x) offsetof(struct vmcs12, x)
-#define FIELD(number, name)	[number] = VMCS12_OFFSET(name)
-#define FIELD64(number, name)	[number] = VMCS12_OFFSET(name), \
-				[number##_HIGH] = VMCS12_OFFSET(name)+4
+#define FIELD(number, name)	[ROL16(number, 6)] = VMCS12_OFFSET(name)
+#define FIELD64(number, name)						\
+	FIELD(number, name),						\
+	[ROL16(number##_HIGH, 6)] = VMCS12_OFFSET(name) + sizeof(u32)
 
 
 static u16 shadow_read_only_fields[] = {
@@ -908,9 +910,13 @@ static const unsigned short vmcs_field_to_offset_table[] = {
 
 static inline short vmcs_field_to_offset(unsigned long field)
 {
-	BUILD_BUG_ON(ARRAY_SIZE(vmcs_field_to_offset_table) > SHRT_MAX);
+	unsigned index;
+
+	if (field >> 15)
+		return -ENOENT;
 
-	if (field >= ARRAY_SIZE(vmcs_field_to_offset_table))
+	index = ROL16(field, 6);
+	if (index >= ARRAY_SIZE(vmcs_field_to_offset_table))
 		return -ENOENT;
 
 	/*
@@ -919,10 +925,10 @@ static inline short vmcs_field_to_offset(unsigned long field)
 	 */
 	asm("lfence");
 
-	if (vmcs_field_to_offset_table[field] == 0)
+	if (vmcs_field_to_offset_table[index] == 0)
 		return -ENOENT;
 
-	return vmcs_field_to_offset_table[field];
+	return vmcs_field_to_offset_table[index];
 }
 
 static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)
--
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