KVM: x86 emulator: access GPRs on demand

Instead of populating the entire register file, read in registers
as they are accessed, and write back only the modified ones.  This
saves a VMREAD and VMWRITE on Intel (for rsp, since it is not usually
used during emulation), and a two 128-byte copies for the registers.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 19 insertions, 1 deletions

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index c764f43b71c5..282aee5d6ac1 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -86,6 +86,19 @@ struct x86_instruction_info {
 
 struct x86_emulate_ops {
         /*
+         * read_gpr: read a general purpose register (rax - r15)
+         *
+         * @reg: gpr number.
+         */
+        ulong (*read_gpr)(struct x86_emulate_ctxt *ctxt, unsigned reg);
+        /*
+         * write_gpr: write a general purpose register (rax - r15)
+         *
+         * @reg: gpr number.
+         * @val: value to write.
+         */
+        void (*write_gpr)(struct x86_emulate_ctxt *ctxt, unsigned reg, ulong val);
+        /*
          * read_std: Read bytes of standard (non-emulated/special) memory.
          *           Used for descriptor reading.
          *  @addr:  [IN ] Linear address from which to read.
@@ -281,8 +294,10 @@ struct x86_emulate_ctxt {
         bool rip_relative;
         unsigned long _eip;
         struct operand memop;
+        u32 regs_valid;  /* bitmaps of registers in _regs[] that can be read */
+        u32 regs_dirty;  /* bitmaps of registers in _regs[] that have been written */
         /* Fields above regs are cleared together. */
-        unsigned long regs[NR_VCPU_REGS];
+        unsigned long _regs[NR_VCPU_REGS];
         struct operand *memopp;
         struct fetch_cache fetch;
         struct read_cache io_read;
@@ -394,4 +409,7 @@ int emulator_task_switch(struct x86_emulate_ctxt *ctxt,
                          u16 tss_selector, int idt_index, int reason,
                          bool has_error_code, u32 error_code);
 int emulate_int_real(struct x86_emulate_ctxt *ctxt, int irq);
+void emulator_invalidate_register_cache(struct x86_emulate_ctxt *ctxt);
+void emulator_writeback_register_cache(struct x86_emulate_ctxt *ctxt);
+
 #endif /* _ASM_X86_KVM_X86_EMULATE_H */