On Fri, Mar 15, 2013 at 08:38:56AM +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>
> Very old user space (namely qemu-kvm before kvm-49) didn't set the TSS
> base before running the VCPU. We always warned about this bug, but no
> reports about users actually seeing this are known. Time to finally
> remove the workaround that effectively prevented to call vmx_vcpu_reset
> while already holding the KVM srcu lock.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Reviewed-by: Gleb Natapov <gleb@xxxxxxxxxx>
> ---
>
> This obsoletes all other attempts to allow vmx_vcpu_reset to be called
> with the srcu lock held. Hope we can settle the topic this way.
>
> arch/x86/kvm/vmx.c | 30 ++++--------------------------
> 1 files changed, 4 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 958ac3a..310bd00 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2898,22 +2898,6 @@ static void enter_pmode(struct kvm_vcpu *vcpu)
> vmx->cpl = 0;
> }
>
> -static gva_t rmode_tss_base(struct kvm *kvm)
> -{
> - if (!kvm->arch.tss_addr) {
> - struct kvm_memslots *slots;
> - struct kvm_memory_slot *slot;
> - gfn_t base_gfn;
> -
> - slots = kvm_memslots(kvm);
> - slot = id_to_memslot(slots, 0);
> - base_gfn = slot->base_gfn + slot->npages - 3;
> -
> - return base_gfn << PAGE_SHIFT;
> - }
> - return kvm->arch.tss_addr;
> -}
> -
> static void fix_rmode_seg(int seg, struct kvm_segment *save)
> {
> const struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];
> @@ -2964,19 +2948,15 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
>
> /*
> * Very old userspace does not call KVM_SET_TSS_ADDR before entering
> - * vcpu. Call it here with phys address pointing 16M below 4G.
> + * vcpu. Warn the user that an update is overdue.
> */
> - if (!vcpu->kvm->arch.tss_addr) {
> + if (!vcpu->kvm->arch.tss_addr)
> printk_once(KERN_WARNING "kvm: KVM_SET_TSS_ADDR need to be "
> "called before entering vcpu\n");
> - srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> - vmx_set_tss_addr(vcpu->kvm, 0xfeffd000);
> - vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> - }
>
> vmx_segment_cache_clear(vmx);
>
> - vmcs_writel(GUEST_TR_BASE, rmode_tss_base(vcpu->kvm));
> + vmcs_writel(GUEST_TR_BASE, vcpu->kvm->arch.tss_addr);
> vmcs_write32(GUEST_TR_LIMIT, RMODE_TSS_SIZE - 1);
> vmcs_write32(GUEST_TR_AR_BYTES, 0x008b);
>
> @@ -3623,7 +3603,7 @@ static int init_rmode_tss(struct kvm *kvm)
> int r, idx, ret = 0;
>
> idx = srcu_read_lock(&kvm->srcu);
> - fn = rmode_tss_base(kvm) >> PAGE_SHIFT;
> + fn = kvm->arch.tss_addr >> PAGE_SHIFT;
> r = kvm_clear_guest_page(kvm, fn, 0, PAGE_SIZE);
> if (r < 0)
> goto out;
> @@ -4190,9 +4170,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
> vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
>
> vmx->vcpu.arch.cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
> - vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> vmx_set_cr0(&vmx->vcpu, kvm_read_cr0(vcpu)); /* enter rmode */
> - srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> vmx_set_cr4(&vmx->vcpu, 0);
> vmx_set_efer(&vmx->vcpu, 0);
> vmx_fpu_activate(&vmx->vcpu);
> --
> 1.7.3.4
--
Gleb.
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