[patch 2/3] KVM: task switch: use seg regs provided by subarch instead of reading from GDT

Marcelo Tosatti
2008-07-16T22:18:43Z

[-- Attachment #1: task-switch-use-virt-seg-info --]
[-- Type: text/plain, Size: 5414 bytes --]

There is no guarantee that the old TSS descriptor in the GDT contains
the proper base address. This is the case for Windows installation's
reboot-via-triplefault.

Use guest registers instead. Also translate the address properly.

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

Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -3278,54 +3278,6 @@ static u32 get_tss_base_addr(struct kvm_
return vcpu->arch.mmu.gva_to_gpa(vcpu, base_addr);
}

-static int load_tss_segment32(struct kvm_vcpu *vcpu,
- struct desc_struct *seg_desc,
- struct tss_segment_32 *tss)
-{
- u32 base_addr;
-
- base_addr = get_tss_base_addr(vcpu, seg_desc);
-
- return kvm_read_guest(vcpu->kvm, base_addr, tss,
- sizeof(struct tss_segment_32));
-}
-
-static int save_tss_segment32(struct kvm_vcpu *vcpu,
- struct desc_struct *seg_desc,
- struct tss_segment_32 *tss)
-{
- u32 base_addr;
-
- base_addr = get_tss_base_addr(vcpu, seg_desc);
-
- return kvm_write_guest(vcpu->kvm, base_addr, tss,
- sizeof(struct tss_segment_32));
-}
-
-static int load_tss_segment16(struct kvm_vcpu *vcpu,
- struct desc_struct *seg_desc,
- struct tss_segment_16 *tss)
-{
- u32 base_addr;
-
- base_addr = get_tss_base_addr(vcpu, seg_desc);
-
- return kvm_read_guest(vcpu->kvm, base_addr, tss,
- sizeof(struct tss_segment_16));
-}
-
-static int save_tss_segment16(struct kvm_vcpu *vcpu,
- struct desc_struct *seg_desc,
- struct tss_segment_16 *tss)
-{
- u32 base_addr;
-
- base_addr = get_tss_base_addr(vcpu, seg_desc);
-
- return kvm_write_guest(vcpu->kvm, base_addr, tss,
- sizeof(struct tss_segment_16));
-}
-
static u16 get_segment_selector(struct kvm_vcpu *vcpu, int seg)
{
struct kvm_segment kvm_seg;
@@ -3482,20 +3434,26 @@ static int load_state_from_tss16(struct
}

static int kvm_task_switch_16(struct kvm_vcpu *vcpu, u16 tss_selector,
- struct desc_struct *cseg_desc,
+ u32 old_tss_base,
struct desc_struct *nseg_desc)
{
struct tss_segment_16 tss_segment_16;
int ret = 0;

- if (load_tss_segment16(vcpu, cseg_desc, &tss_segment_16))
+ if (kvm_read_guest(vcpu->kvm, old_tss_base, &tss_segment_16,
+ sizeof tss_segment_16))
goto out;

save_state_to_tss16(vcpu, &tss_segment_16);
- save_tss_segment16(vcpu, cseg_desc, &tss_segment_16);

- if (load_tss_segment16(vcpu, nseg_desc, &tss_segment_16))
+ if (kvm_write_guest(vcpu->kvm, old_tss_base, &tss_segment_16,
+ sizeof tss_segment_16))
goto out;
+
+ if (kvm_read_guest(vcpu->kvm, get_tss_base_addr(vcpu, nseg_desc),
+ &tss_segment_16, sizeof tss_segment_16))
+ goto out;
+
if (load_state_from_tss16(vcpu, &tss_segment_16))
goto out;

@@ -3505,20 +3463,26 @@ out:
}

static int kvm_task_switch_32(struct kvm_vcpu *vcpu, u16 tss_selector,
- struct desc_struct *cseg_desc,
+ u32 old_tss_base,
struct desc_struct *nseg_desc)
{
struct tss_segment_32 tss_segment_32;
int ret = 0;

- if (load_tss_segment32(vcpu, cseg_desc, &tss_segment_32))
+ if (kvm_read_guest(vcpu->kvm, old_tss_base, &tss_segment_32,
+ sizeof tss_segment_32))
goto out;

save_state_to_tss32(vcpu, &tss_segment_32);
- save_tss_segment32(vcpu, cseg_desc, &tss_segment_32);

- if (load_tss_segment32(vcpu, nseg_desc, &tss_segment_32))
+ if (kvm_write_guest(vcpu->kvm, old_tss_base, &tss_segment_32,
+ sizeof tss_segment_32))
+ goto out;
+
+ if (kvm_read_guest(vcpu->kvm, get_tss_base_addr(vcpu, nseg_desc),
+ &tss_segment_32, sizeof tss_segment_32))
goto out;
+
if (load_state_from_tss32(vcpu, &tss_segment_32))
goto out;

@@ -3533,16 +3497,20 @@ int kvm_task_switch(struct kvm_vcpu *vcp
struct desc_struct cseg_desc;
struct desc_struct nseg_desc;
int ret = 0;
+ u32 old_tss_base = get_segment_base(vcpu, VCPU_SREG_TR);
+ u16 old_tss_sel = get_segment_selector(vcpu, VCPU_SREG_TR);

- kvm_get_segment(vcpu, &tr_seg, VCPU_SREG_TR);
+ old_tss_base = vcpu->arch.mmu.gva_to_gpa(vcpu, old_tss_base);

+ /* FIXME: Handle errors. Failure to read either TSS or their
+ * descriptors should generate a pagefault.
+ */
if (load_guest_segment_descriptor(vcpu, tss_selector, &nseg_desc))
goto out;

- if (load_guest_segment_descriptor(vcpu, tr_seg.selector, &cseg_desc))
+ if (load_guest_segment_descriptor(vcpu, old_tss_sel, &cseg_desc))
goto out;

-
if (reason != TASK_SWITCH_IRET) {
int cpl;

@@ -3560,8 +3528,7 @@ int kvm_task_switch(struct kvm_vcpu *vcp

if (reason == TASK_SWITCH_IRET || reason == TASK_SWITCH_JMP) {
cseg_desc.type &= ~(1 << 1); //clear the B flag
- save_guest_segment_descriptor(vcpu, tr_seg.selector,
- &cseg_desc);
+ save_guest_segment_descriptor(vcpu, old_tss_sel, &cseg_desc);
}

if (reason == TASK_SWITCH_IRET) {
@@ -3572,10 +3539,10 @@ int kvm_task_switch(struct kvm_vcpu *vcp
kvm_x86_ops->skip_emulated_instruction(vcpu);

if (nseg_desc.type & 8)
- ret = kvm_task_switch_32(vcpu, tss_selector, &cseg_desc,
+ ret = kvm_task_switch_32(vcpu, tss_selector, old_tss_base,
&nseg_desc);
else
- ret = kvm_task_switch_16(vcpu, tss_selector, &cseg_desc,
+ ret = kvm_task_switch_16(vcpu, tss_selector, old_tss_base,
&nseg_desc);

if (reason == TASK_SWITCH_CALL || reason == TASK_SWITCH_GATE) {

--