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KVM: VMX: Let gcc to choose which registers to save (x86_64)

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This patch lets GCC to determine which registers to save when we
switch to/from a VCPU in the case of intel x86_64.

* Original code saves following registers:

    rax, rbx, rcx, rdx, rsi, rdi, rbp,
    r8, r9, r10, r11, r12, r13, r14, r15

* Patched code:

  - informs GCC that we modify following registers
    using the clobber description:

    rbx, rdi, rsi,
    r8, r9, r10, r11, r12, r13, r14, r15

  - doesn't save rax because it is an output operand (vmx->fail)

  - cannot put rcx in clobber description because it is an input operand,
    but as we modify it and we want to keep its value (vcpu), we must
    save it (pop/push)

  - rbp is saved (pop/push) because GCC seems to ignore its use in the clobber
    description.

  - rdx is saved (pop/push) because it is reserved by GCC (REGPARM) and
    cannot be put in the clobber description.

  - line "mov (%%rsp), %3 \n\t" has been removed because %3
    is rcx and rcx is restored just after.

  - line ASM_VMX_VMWRITE_RSP_RDX() is moved out of the ifdef/else/endif

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Laurent Vivier 2007-10-25 14:18:52 +02:00 committed by Avi Kivity
parent cbc9402297
commit c20363006a
1 changed files with 9 additions and 12 deletions
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21
drivers/kvm/vmx.c
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@ -2265,16 +2265,12 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
asm(
/* Store host registers */
#ifdef CONFIG_X86_64
"push %%rax; push %%rbx; push %%rdx;"
"push %%rsi; push %%rdi; push %%rbp;"
"push %%r8; push %%r9; push %%r10; push %%r11;"
"push %%r12; push %%r13; push %%r14; push %%r15;"
"push %%rdx; push %%rbp;"
"push %%rcx \n\t"
ASM_VMX_VMWRITE_RSP_RDX "\n\t"
#else
"pusha; push %%ecx \n\t"
ASM_VMX_VMWRITE_RSP_RDX "\n\t"
#endif
ASM_VMX_VMWRITE_RSP_RDX "\n\t"
/* Check if vmlaunch of vmresume is needed */
"cmp $0, %1 \n\t"
/* Load guest registers. Don't clobber flags. */
@ -2333,12 +2329,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
"mov %%r15, %c[r15](%3) \n\t"
"mov %%cr2, %%rax \n\t"
"mov %%rax, %c[cr2](%3) \n\t"
"mov (%%rsp), %3 \n\t"
"pop %%rcx; pop %%r15; pop %%r14; pop %%r13; pop %%r12;"
"pop %%r11; pop %%r10; pop %%r9; pop %%r8;"
"pop %%rbp; pop %%rdi; pop %%rsi;"
"pop %%rdx; pop %%rbx; pop %%rax \n\t"
"pop %%rcx; pop %%rbp; pop %%rdx \n\t"
#else
"xchg %3, (%%esp) \n\t"
"mov %%eax, %c[rax](%3) \n\t"
@ -2376,7 +2368,12 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
[r15]"i"(offsetof(struct kvm_vcpu, regs[VCPU_REGS_R15])),
#endif
[cr2]"i"(offsetof(struct kvm_vcpu, cr2))
: "cc", "memory");
: "cc", "memory"
#ifdef CONFIG_X86_64
, "rbx", "rdi", "rsi"
, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
#endif
);
vcpu->interrupt_window_open =
(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & 3) == 0;