From: Greg KH <greg@kroah.com>
To: Sasha Levin <sashal@kernel.org>
Cc: stable@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
Jinwoo Lee <rkskek9254@gmail.com>,
Stefan Teodorescu <fane@google.com>
Subject: Re: [PATCH 6.18.y 4/4] KVM: x86: Fill kvm_run exit fields in common get_nested_state_pages() error paths
Date: Wed, 7 Oct 2026 08:40:40 +0200 [thread overview]
Message-ID: <2026100736-rack-shimmy-fe09@gregkh> (raw)
In-Reply-To: <20260930153934.2895211-4-sashal@kernel.org>
On Wed, Sep 30, 2026 at 11:39:34AM -0400, Sasha Levin wrote:
> From: Sean Christopherson <seanjc@google.com>
>
> [ Upstream commit c1214f293d77c6e425a379f90d09bdb4815993a8 ]
>
> Fill kvm_run with "internal error, emulation" in the common error handling
> paths for getting nested state pages, as requiring each check to manually
> fill kvm_run is error prone and requires a non-trivial amount of copy+paste.
>
> Specifically, both SVM and VMX fail to fill kvm_run if load_pdptrs() fails,
> and SVM fails to fill kvm_run if kvm_hv_verify_vp_assist() fails. If those
> flows fail, the *best* case scenario is that KVM will exit to userspace
> with KVM_EXIT_UNKNOWN. The worst case scenario is that KVM exits with a
> stale exit_reason and confuses userspace.
>
> Note, SVM never exits to userspace if something goes sideways when dealing
> with vmcb12 assets while emulating VMRUN, i.e. lack of SVM-specific code is
> not a bug.
>
> Fixes: 0f85722341b0 ("KVM: nVMX: delay loading of PDPTRs to KVM_REQ_GET_NESTED_STATE_PAGES")
> Fixes: 232f75d3b4b5 ("KVM: nSVM: call nested_svm_load_cr3 on nested state load")
> Fixes: 3f4a812edf5c ("KVM: nSVM: hyper-v: Enable L2 TLB flush")
> Cc: stable@vger.kernel.org
> Reported-by: Jinwoo Lee <rkskek9254@gmail.com>
> Closes: https://lore.kernel.org/all/20260813043932.3214460-1-rkskek9254@gmail.com
> Reported-by: Stefan Teodorescu <fane@google.com>
> Link: https://patch.msgid.link/20260921211608.1030158-3-seanjc@google.com
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> arch/x86/kvm/svm/nested.c | 7 +------
> arch/x86/kvm/vmx/nested.c | 15 +++++----------
> arch/x86/kvm/x86.c | 3 +++
> 3 files changed, 9 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index c765ea1dff69c..a6b92819318b8 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1953,13 +1953,8 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
> return false;
> }
>
> - if (!nested_svm_merge_msrpm(vcpu)) {
> - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> - vcpu->run->internal.suberror =
> - KVM_INTERNAL_ERROR_EMULATION;
> - vcpu->run->internal.ndata = 0;
> + if (!nested_svm_merge_msrpm(vcpu))
> return false;
> - }
>
> if (kvm_hv_verify_vp_assist(vcpu))
> return false;
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index cb44ae23728b3..890ee82af35d6 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3492,10 +3492,6 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
> } else {
> pr_debug_ratelimited("%s: no backing for APIC-access address in vmcs12\n",
> __func__);
> - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> - vcpu->run->internal.suberror =
> - KVM_INTERNAL_ERROR_EMULATION;
> - vcpu->run->internal.ndata = 0;
> return false;
> }
> }
> @@ -3566,11 +3562,6 @@ static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
> if (!nested_get_evmcs_page(vcpu)) {
> pr_debug_ratelimited("%s: enlightened vmptrld failed\n",
> __func__);
> - vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> - vcpu->run->internal.suberror =
> - KVM_INTERNAL_ERROR_EMULATION;
> - vcpu->run->internal.ndata = 0;
> -
> return false;
> }
> #endif
> @@ -3956,8 +3947,12 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>
> vmentry_failed:
> vcpu->arch.nested_run_pending = 0;
> - if (status == NVMX_VMENTRY_KVM_INTERNAL_ERROR)
> + if (status == NVMX_VMENTRY_KVM_INTERNAL_ERROR) {
> + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> + vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
> + vcpu->run->internal.ndata = 0;
> return 0;
> + }
> if (status == NVMX_VMENTRY_VMEXIT)
> return 1;
> WARN_ON_ONCE(status != NVMX_VMENTRY_VMFAIL);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 69d48df5d1d89..c86b828ca578a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10708,6 +10708,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>
> if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
> if (unlikely(!kvm_nested_call(get_nested_state_pages)(vcpu))) {
> + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> + vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
> + vcpu->run->internal.ndata = 0;
> kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
> r = 0;
> goto out;
> --
> 2.53.0
>
>
Did not apply :(
prev parent reply other threads:[~2026-10-07 6:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-29 11:38 FAILED: patch "[PATCH] KVM: x86: Fill kvm_run exit fields in common" failed to apply to 6.18-stable tree gregkh
2026-09-30 15:39 ` [PATCH 6.18.y 1/4] KVM: move TSS constants from kvm_host.h to tss.h Sasha Levin
2026-09-30 15:39 ` [PATCH 6.18.y 2/4] KVM: x86: Reject nested CAP enablement if nested virtualization is disabled Sasha Levin
2026-09-30 15:39 ` [PATCH 6.18.y 3/4] KVM: x86: Add static calls for nested virtualization ops Sasha Levin
2026-09-30 15:39 ` [PATCH 6.18.y 4/4] KVM: x86: Fill kvm_run exit fields in common get_nested_state_pages() error paths Sasha Levin
2026-10-07 6:40 ` Greg KH [this message]
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