commit c12f2b990c7dd7cd6c36e50b0aa71bfad95b4188
parent 1629595c7ee3cc336b5685c9c3630e7f9a11648c
Author: Louis Burda <quent.burda@gmail.com>
Date: Mon, 6 Feb 2023 15:42:46 -0600
Save registers to xmm to lower baseline counts and avoid timing issues with apic_oneshot
Swapping general-purpose registers with xmm registers should be constant-time, while writing and reading from memory after prime will cause cache misses with varying servicing time. This added uncertainty decreases stepping accuracy with apic.
Diffstat:
1 file changed, 45 insertions(+), 46 deletions(-)
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
@@ -31,61 +31,63 @@
#include "../cachepc/macro.S"
-.extern cpc_msrmts
-.extern cpc_regs_tmp
-.extern cpc_regs_vm
+.macro apply_regs func
+ \func %rax %xmm0
+ \func %rbx %xmm1
+ \func %rcx %xmm2
+ \func %rdx %xmm3
+ \func %rbp %xmm4
+ \func %rsp %xmm5
+ \func %rdi %xmm6
+ \func %rsi %xmm7
+ \func %r8 %xmm8
+ \func %r9 %xmm9
+ \func %r10 %xmm10
+ \func %r11 %xmm11
+ \func %r12 %xmm12
+ \func %r13 %xmm13
+ \func %r14 %xmm14
+.endm
-.macro load_tmp off reg
- mov cpc_regs_tmp+\off, \reg
+.macro save_reg src dst
+ movq \src, \dst
.endm
-.macro save_tmp off reg
- mov \reg, cpc_regs_tmp+\off
+.macro swap_reg src dst
+ movq \src, %r15
+ movq \dst, \src
+ movq %r15, \dst
.endm
-.macro load_vm off reg
- mov cpc_regs_vm+\off, \reg
+.macro save_vm
+ apply_regs save_reg
.endm
-.macro save_vm off reg
- mov \reg, cpc_regs_vm+\off
+.macro exit_vm
+ apply_regs swap_reg
.endm
-.macro apply_regs func
- \func 0x00 %rax
- \func 0x08 %rbx
- \func 0x10 %rcx
- \func 0x18 %rdx
- \func 0x20 %rbp
- \func 0x28 %rsp
- \func 0x30 %rdi
- \func 0x38 %rsi
- \func 0x40 %r8
- \func 0x48 %r9
- \func 0x50 %r10
- \func 0x58 %r11
- \func 0x60 %r12
- \func 0x68 %r13
- \func 0x70 %r14
- \func 0x78 %r15
+.macro enter_vm
+ apply_regs swap_reg
+ movq %xmm15, %r15 # fixup tmp reg
.endm
.macro wrap_prime name
- apply_regs save_vm
- apply_regs load_tmp
+ exit_vm
# read vars before prime
xor %rax, %rax
movb cpc_apic_oneshot, %al
- mov %rax, %r12
+ mov %rax, %r11
mov cpc_apic_timer, %eax
- mov %rax, %r13
+ mov %rax, %r12
mov cpc_apic_timer_softdiv, %eax
- mov %rax, %r14
+ mov %rax, %r13
movb cpc_prime_probe, %al
- mov %rax, %r15
+ mov %rax, %r14
# do prime
+ mov %r14, %rax
cmp $0, %al
je skip_prime_\name
wbinvd
@@ -96,7 +98,7 @@
skip_prime_\name:
# do oneshot
- mov %r12, %rax
+ mov %r11, %rax
cmp $0, %al
je skip_apic_\name
# asm from cpc_apic_oneshot_run
@@ -105,28 +107,25 @@ skip_prime_\name:
mov $0x0b, %edx
mov %edx, 0xffffffffff5fd3e0
xor %edx, %edx
- mov %r13, %rax
- div %r14
+ mov %r12, %rax
+ div %r13
mov %eax, 0xffffffffff5fd380
skip_apic_\name:
- apply_regs save_tmp
- apply_regs load_vm
+ enter_vm
.endm
.macro wrap_probe name
- apply_regs save_vm
- apply_regs load_tmp
+ exit_vm
# do probe
- mov %r15, %rax
+ mov %r14, %rax
cmp $0, %al
je skip_probe_\name
probe \name %r8 %r9 %r10 %r11 %r12
skip_probe_\name:
- apply_regs save_tmp
- apply_regs load_vm
+ enter_vm
.endm
@@ -136,7 +135,7 @@ skip_probe_\name:
* @regs: unsigned long * (to guest registers)
*/
SYM_FUNC_START(__svm_vcpu_run)
- apply_regs save_tmp
+ save_vm
push %_ASM_BP
#ifdef CONFIG_X86_64
@@ -269,7 +268,7 @@ SYM_FUNC_END(__svm_vcpu_run)
* @vmcb_pa: unsigned long
*/
SYM_FUNC_START(__svm_sev_es_vcpu_run)
- apply_regs save_tmp
+ save_vm
push %_ASM_BP
#ifdef CONFIG_X86_64
