Avi Kivity a écrit :
> Laurent Vivier wrote:
>> As x86_64 ABI defines some registers saved by the calling function, it
>> is not
>> needed to save all registers in the called function when switching to
>> VCPU.
>> (see http://www.x86-64.org/documentation/abi.pdf, chapter 3.2.1)
>>
>> The best way to do that is to inform GCC which registers we use and let
>> it to save only needed registers.
>>
>>
>
> Strange, yesterday I started to do the same thing but dropped it after I
> got discouraged by reload errors from gcc.
In french, we say "Les beaux esprits se rencontrent" (Voltaire) ;-)
("Great minds think alike")
>> diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
>> index 2c6b64a..d6c91ac 100644
>> --- a/drivers/kvm/vmx.c
>> +++ b/drivers/kvm/vmx.c
>> @@ -2243,16 +2243,12 @@ 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. */
>> @@ -2311,12 +2307,8 @@ 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"
>> @@ -2354,7 +2346,12 @@ 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
>> + );
>>
>
> The comma after "memory" worries me. Can you compile-test on i386?
You're right, I thought I've corrected this. I rework this and test on i386.
> Other than that the patch is very welcome -- the excessive register
> saving is very annoying to me.
I think we can do the same thing with svm.c, but I can't test it.
Regards,
Laurent
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