On 21/12/2017 21:46, Jim Mattson wrote:
> 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. Using a
> three-dimensional table indexed by VMCS field index, VMCS field type,
> and VMCS field width, it's relatively easy to reduce that table to 768
> bytes.
Would it be faster if, instead of the three-dimensional table, we
indexed the array by
((field >> 10) | ((field << 5) & 0x3ff))
which would waste one bit, but still reduce the table a lot.
Alternatively, it could use rotate-right-16(field, 10):
(u16)((field >> 10) | ((field << 6))
That would waste two bits, but it would faster still to build the index.
Paolo
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 145 ++++++++++++++++++++++++++++++++---------------------
> 1 file changed, 88 insertions(+), 57 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 1847000fbb0c..bd601b0984d1 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -714,11 +714,15 @@ static struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
> return &(to_vmx(vcpu)->pi_desc);
> }
>
> -#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 VMCS_FIELD_HIGH(field) ((field) & 1)
> +#define VMCS_FIELD_INDEX(field) (((field) >> 1) & 0x1ff)
> +#define VMCS_FIELD_TYPE(field) (((field) >> 10) & 3)
> +#define VMCS_FIELD_WIDTH(field) (((field) >> 13) & 3)
>
> +#define VMCS12_OFFSET(x) offsetof(struct vmcs12, x)
> +#define FIELD(n, name) \
> + [VMCS_FIELD_INDEX(n)][VMCS_FIELD_TYPE(n)][VMCS_FIELD_WIDTH(n)] = \
> + VMCS12_OFFSET(name)
>
> static unsigned long shadow_read_only_fields[] = {
> /*
> @@ -779,7 +783,7 @@ static unsigned long shadow_read_write_fields[] = {
> static int max_shadow_read_write_fields =
> ARRAY_SIZE(shadow_read_write_fields);
>
> -static const unsigned short vmcs_field_to_offset_table[] = {
> +static const unsigned short vmcs_field_to_offset_table[][4][4] = {
> FIELD(VIRTUAL_PROCESSOR_ID, virtual_processor_id),
> FIELD(POSTED_INTR_NV, posted_intr_nv),
> FIELD(GUEST_ES_SELECTOR, guest_es_selector),
> @@ -799,39 +803,39 @@ static const unsigned short vmcs_field_to_offset_table[] = {
> FIELD(HOST_FS_SELECTOR, host_fs_selector),
> FIELD(HOST_GS_SELECTOR, host_gs_selector),
> FIELD(HOST_TR_SELECTOR, host_tr_selector),
> - FIELD64(IO_BITMAP_A, io_bitmap_a),
> - FIELD64(IO_BITMAP_B, io_bitmap_b),
> - FIELD64(MSR_BITMAP, msr_bitmap),
> - FIELD64(VM_EXIT_MSR_STORE_ADDR, vm_exit_msr_store_addr),
> - FIELD64(VM_EXIT_MSR_LOAD_ADDR, vm_exit_msr_load_addr),
> - FIELD64(VM_ENTRY_MSR_LOAD_ADDR, vm_entry_msr_load_addr),
> - FIELD64(TSC_OFFSET, tsc_offset),
> - FIELD64(VIRTUAL_APIC_PAGE_ADDR, virtual_apic_page_addr),
> - FIELD64(APIC_ACCESS_ADDR, apic_access_addr),
> - FIELD64(POSTED_INTR_DESC_ADDR, posted_intr_desc_addr),
> - FIELD64(VM_FUNCTION_CONTROL, vm_function_control),
> - FIELD64(EPT_POINTER, ept_pointer),
> - FIELD64(EOI_EXIT_BITMAP0, eoi_exit_bitmap0),
> - FIELD64(EOI_EXIT_BITMAP1, eoi_exit_bitmap1),
> - FIELD64(EOI_EXIT_BITMAP2, eoi_exit_bitmap2),
> - FIELD64(EOI_EXIT_BITMAP3, eoi_exit_bitmap3),
> - FIELD64(EPTP_LIST_ADDRESS, eptp_list_address),
> - FIELD64(XSS_EXIT_BITMAP, xss_exit_bitmap),
> - FIELD64(GUEST_PHYSICAL_ADDRESS, guest_physical_address),
> - FIELD64(VMCS_LINK_POINTER, vmcs_link_pointer),
> - FIELD64(PML_ADDRESS, pml_address),
> - FIELD64(GUEST_IA32_DEBUGCTL, guest_ia32_debugctl),
> - FIELD64(GUEST_IA32_PAT, guest_ia32_pat),
> - FIELD64(GUEST_IA32_EFER, guest_ia32_efer),
> - FIELD64(GUEST_IA32_PERF_GLOBAL_CTRL, guest_ia32_perf_global_ctrl),
> - FIELD64(GUEST_PDPTR0, guest_pdptr0),
> - FIELD64(GUEST_PDPTR1, guest_pdptr1),
> - FIELD64(GUEST_PDPTR2, guest_pdptr2),
> - FIELD64(GUEST_PDPTR3, guest_pdptr3),
> - FIELD64(GUEST_BNDCFGS, guest_bndcfgs),
> - FIELD64(HOST_IA32_PAT, host_ia32_pat),
> - FIELD64(HOST_IA32_EFER, host_ia32_efer),
> - FIELD64(HOST_IA32_PERF_GLOBAL_CTRL, host_ia32_perf_global_ctrl),
> + FIELD(IO_BITMAP_A, io_bitmap_a),
> + FIELD(IO_BITMAP_B, io_bitmap_b),
> + FIELD(MSR_BITMAP, msr_bitmap),
> + FIELD(VM_EXIT_MSR_STORE_ADDR, vm_exit_msr_store_addr),
> + FIELD(VM_EXIT_MSR_LOAD_ADDR, vm_exit_msr_load_addr),
> + FIELD(VM_ENTRY_MSR_LOAD_ADDR, vm_entry_msr_load_addr),
> + FIELD(TSC_OFFSET, tsc_offset),
> + FIELD(VIRTUAL_APIC_PAGE_ADDR, virtual_apic_page_addr),
> + FIELD(APIC_ACCESS_ADDR, apic_access_addr),
> + FIELD(POSTED_INTR_DESC_ADDR, posted_intr_desc_addr),
> + FIELD(VM_FUNCTION_CONTROL, vm_function_control),
> + FIELD(EPT_POINTER, ept_pointer),
> + FIELD(EOI_EXIT_BITMAP0, eoi_exit_bitmap0),
> + FIELD(EOI_EXIT_BITMAP1, eoi_exit_bitmap1),
> + FIELD(EOI_EXIT_BITMAP2, eoi_exit_bitmap2),
> + FIELD(EOI_EXIT_BITMAP3, eoi_exit_bitmap3),
> + FIELD(EPTP_LIST_ADDRESS, eptp_list_address),
> + FIELD(XSS_EXIT_BITMAP, xss_exit_bitmap),
> + FIELD(GUEST_PHYSICAL_ADDRESS, guest_physical_address),
> + FIELD(VMCS_LINK_POINTER, vmcs_link_pointer),
> + FIELD(PML_ADDRESS, pml_address),
> + FIELD(GUEST_IA32_DEBUGCTL, guest_ia32_debugctl),
> + FIELD(GUEST_IA32_PAT, guest_ia32_pat),
> + FIELD(GUEST_IA32_EFER, guest_ia32_efer),
> + FIELD(GUEST_IA32_PERF_GLOBAL_CTRL, guest_ia32_perf_global_ctrl),
> + FIELD(GUEST_PDPTR0, guest_pdptr0),
> + FIELD(GUEST_PDPTR1, guest_pdptr1),
> + FIELD(GUEST_PDPTR2, guest_pdptr2),
> + FIELD(GUEST_PDPTR3, guest_pdptr3),
> + FIELD(GUEST_BNDCFGS, guest_bndcfgs),
> + FIELD(HOST_IA32_PAT, host_ia32_pat),
> + FIELD(HOST_IA32_EFER, host_ia32_efer),
> + FIELD(HOST_IA32_PERF_GLOBAL_CTRL, host_ia32_perf_global_ctrl),
> FIELD(PIN_BASED_VM_EXEC_CONTROL, pin_based_vm_exec_control),
> FIELD(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control),
> FIELD(EXCEPTION_BITMAP, exception_bitmap),
> @@ -923,15 +927,56 @@ static const unsigned short vmcs_field_to_offset_table[] = {
> FIELD(HOST_RIP, host_rip),
> };
>
> +enum vmcs_field_width {
> + VMCS_FIELD_WIDTH_U16 = 0,
> + VMCS_FIELD_WIDTH_U64 = 1,
> + VMCS_FIELD_WIDTH_U32 = 2,
> + VMCS_FIELD_WIDTH_NATURAL_WIDTH = 3
> +};
> +
> +static inline int vmcs_field_width(unsigned long field)
> +{
> + if (VMCS_FIELD_HIGH(field)) /* the *_HIGH fields are all 32 bit */
> + return VMCS_FIELD_WIDTH_U32;
> + return VMCS_FIELD_WIDTH(field);
> +}
> +
> +enum vmcs_field_type {
> + VMCS_FIELD_TYPE_CONTROL = 0,
> + VMCS_FIELD_TYPE_INFO = 1,
> + VMCS_FIELD_TYPE_GUEST = 2,
> + VMCS_FIELD_TYPE_HOST = 3
> +};
> +
> +static inline int vmcs_field_type(unsigned long field)
> +{
> + return VMCS_FIELD_TYPE(field);
> +}
> +
> static inline short vmcs_field_to_offset(unsigned long field)
> {
> - BUILD_BUG_ON(ARRAY_SIZE(vmcs_field_to_offset_table) > SHRT_MAX);
> + unsigned index = VMCS_FIELD_INDEX(field);
> + unsigned type = VMCS_FIELD_TYPE(field);
> + unsigned width = VMCS_FIELD_WIDTH(field);
> + short offset;
>
> - if (field >= ARRAY_SIZE(vmcs_field_to_offset_table) ||
> - vmcs_field_to_offset_table[field] == 0)
> + BUILD_BUG_ON(ARRAY_SIZE(vmcs_field_to_offset_table) >
> + VMCS12_MAX_FIELD_INDEX + 1);
> + if (VMCS_FIELD_HIGH(field) && width != VMCS_FIELD_WIDTH_U64)
> return -ENOENT;
>
> - return vmcs_field_to_offset_table[field];
> + if (index >= ARRAY_SIZE(vmcs_field_to_offset_table))
> + return -ENOENT;
> +
> + offset = vmcs_field_to_offset_table[index][type][width];
> +
> + if (offset == 0)
> + return -ENOENT;
> +
> + if (VMCS_FIELD_HIGH(field))
> + offset += sizeof(u32);
> +
> + return offset;
> }
>
> static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)
> @@ -4050,23 +4095,9 @@ static void free_kvm_area(void)
> }
> }
>
> -enum vmcs_field_width {
> - VMCS_FIELD_WIDTH_U16 = 0,
> - VMCS_FIELD_WIDTH_U64 = 1,
> - VMCS_FIELD_WIDTH_U32 = 2,
> - VMCS_FIELD_WIDTH_NATURAL_WIDTH = 3
> -};
> -
> -static inline int vmcs_field_width(unsigned long field)
> -{
> - if (0x1 & field) /* the *_HIGH fields are all 32 bit */
> - return VMCS_FIELD_WIDTH_U32;
> - return (field >> 13) & 0x3 ;
> -}
> -
> static inline int vmcs_field_readonly(unsigned long field)
> {
> - return (((field >> 10) & 0x3) == 1);
> + return VMCS_FIELD_TYPE(field) == VMCS_FIELD_TYPE_INFO;
> }
>
> static void init_vmcs_shadow_fields(void)
>
