A question about how kvm switch context to guest
Hi kashyapc & all,
I see a piece of code in vmx_vcpu_run as below, is it used to switch context to a guest? Kvm don't used "vmlaunch" or "vmresume" to launch or resume a guest? Why does kvm need to manually switch context by filling registers using stored register copies?
===============
asm(
/* Store host registers */
"push %%"R"dx; push %%"R"bp;"
"push %%"R"cx \n\t" /* placeholder for guest rcx */
"push %%"R"cx \n\t"
"cmp %%"R"sp, %c[host_rsp](%0) \n\t"
"je 1f \n\t"
"mov %%"R"sp, %c[host_rsp](%0) \n\t"
__ex(ASM_VMX_VMWRITE_RSP_RDX) "\n\t"
"1: \n\t"
/* Reload cr2 if changed */
"mov %c[cr2](%0), %%"R"ax \n\t"
"mov %%cr2, %%"R"dx \n\t"
"cmp %%"R"ax, %%"R"dx \n\t"
"je 2f \n\t"
"mov %%"R"ax, %%cr2 \n\t"
"2: \n\t"
/* Check if vmlaunch of vmresume is needed */
"cmpl $0, %c[launched](%0) \n\t"
/* Load guest registers. Don't clobber flags. */
"mov %c[rax](%0), %%"R"ax \n\t"
"mov %c[rbx](%0), %%"R"bx \n\t"
"mov %c[rdx](%0), %%"R"dx \n\t"
"mov %c[rsi](%0), %%"R"si \n\t"
"mov %c[rdi](%0), %%"R"di \n\t"
"mov %c[rbp](%0), %%"R"bp \n\t"========
Thanks,
Zhengwang
Quoted 5 lines · Zhengwang Ruan
Hi kashyapc & all,
I see a piece of code in
vmx_vcpu_runas below, is it used to switch context to a guest? Kvm don't used "vmlaunch" or "vmresume" to launch or resume a guest?
You trimmed the bit that contains vmlaunch/vmresume.
Why does kvm need to manually switch context by filling
Quoted 1 line
registers using stored register copies?
Those registers don't get automatically switched by the hardware.
Quoted 30 lines
===============
asm(
/* Store host registers */ "push %%"R"dx; push %%"R"bp;" "push %%"R"cx \n\t" /* placeholder for guest rcx */ "push %%"R"cx \n\t" "cmp %%"R"sp, %c[host_rsp](%0) \n\t" "je 1f \n\t" "mov %%"R"sp, %c[host_rsp](%0) \n\t" __ex(ASM_VMX_VMWRITE_RSP_RDX) "\n\t" "1: \n\t" /* Reload cr2 if changed */ "mov %c[cr2](%0), %%"R"ax \n\t" "mov %%cr2, %%"R"dx \n\t" "cmp %%"R"ax, %%"R"dx \n\t" "je 2f \n\t" "mov %%"R"ax, %%cr2 \n\t" "2: \n\t" /* Check if vmlaunch of vmresume is needed */ "cmpl $0, %c[launched](%0) \n\t" /* Load guest registers. Don't clobber flags. */ "mov %c[rax](%0), %%"R"ax \n\t" "mov %c[rbx](%0), %%"R"bx \n\t" "mov %c[rdx](%0), %%"R"dx \n\t" "mov %c[rsi](%0), %%"R"si \n\t" "mov %c[rdi](%0), %%"R"di \n\t" "mov %c[rbp](%0), %%"R"bp \n\t"
Signature · 1 line
error compiling committee.c: too many arguments to function
-------- Original Message --------
From: Avi Kivity
Sent: 2012年07月04日 星期三 16时47分40秒
To: Zhengwang Ruan
Subject: Re: A question about how kvm switch context to guest
Quoted 11 lines · Zhengwang Ruan
Quoted 5 lines
Hi kashyapc& all,
I see a piece of code in
vmx_vcpu_runas below, is it used to switch context to a guest? Kvm don't used "vmlaunch" or "vmresume" to launch or resume a guest?You trimmed the bit that contains vmlaunch/vmresume.
Why does kvm need to manually switch context by filling
Quoted 1 line
registers using stored register copies?
Those registers don't get automatically switched by the hardware.
Avi,
got it! thank you!
Regards,
Zhengwang
Quoted 31 lines
Quoted 30 lines
===============
asm(
/* Store host registers */ "push %%"R"dx; push %%"R"bp;" "push %%"R"cx \n\t" /* placeholder for guest rcx */ "push %%"R"cx \n\t" "cmp %%"R"sp, %c[host_rsp](%0) \n\t" "je 1f \n\t" "mov %%"R"sp, %c[host_rsp](%0) \n\t" __ex(ASM_VMX_VMWRITE_RSP_RDX) "\n\t" "1: \n\t" /* Reload cr2 if changed */ "mov %c[cr2](%0), %%"R"ax \n\t" "mov %%cr2, %%"R"dx \n\t" "cmp %%"R"ax, %%"R"dx \n\t" "je 2f \n\t" "mov %%"R"ax, %%cr2 \n\t" "2: \n\t" /* Check if vmlaunch of vmresume is needed */ "cmpl $0, %c[launched](%0) \n\t" /* Load guest registers. Don't clobber flags. */ "mov %c[rax](%0), %%"R"ax \n\t" "mov %c[rbx](%0), %%"R"bx \n\t" "mov %c[rdx](%0), %%"R"dx \n\t" "mov %c[rsi](%0), %%"R"si \n\t" "mov %c[rdi](%0), %%"R"di \n\t" "mov %c[rbp](%0), %%"R"bp \n\t"