On 2/25/2020 2:13 PM, Sean Christopherson wrote:
On Tue, Feb 25, 2020 at 08:13:15AM +0800, Xiaoyao Li wrote:
On 2/25/2020 12:17 AM, Sean Christopherson wrote:
On Mon, Feb 24, 2020 at 02:04:46PM +0100, Vitaly Kuznetsov wrote:
Xiaoyao Li <xiaoyao.li@xxxxxxxxx> writes:
On 2/24/2020 6:16 PM, Vitaly Kuznetsov wrote:
Xiaoyao Li <xiaoyao.li@xxxxxxxxx> writes:
Here variable basic_exit_reason is added for the cases where only basic
exit reason number is needed.
Can we do the other way around, i.e. introduce 'extended_exit_reason'
and use it where all 32 bits are needed? I'm fine with the change, just
trying to minimize the (unneeded) code churn.
100% agree. Even better than adding a second field to vcpu_vmx would be
to make it a union, though we'd probably want to call it something like
full_exit_reason in that case. That should give us compile-time checks on
exit_reason, e.g. if we try to query one of the upper bits using a u16, e.g.
I have thought about union, but it seems
union {
u16 exit_reason;
u32 full_exit_reason;
}
is not a good name. Since there are many codes in vmx.c and nested.c assume
that exit_reason stands for 32-bit EXIT REASON vmcs field as well as
evmcs->vm_exit_reason and vmcs12->vm_exit_reason. Do we really want to also
rename them to full_exit_reason?
It's actually the opposite, almost all of the VMX code assumes exit_reason
holds only the basic exit reason, i.e. a 16-bit value. For example, SGX
adds a modifier flag to denote a VM-Exit was from enclave mode, and that
bit needs to be stripped from exit_reason, otherwise all the checks like
"if (exit_reason == blah_blah_blah)" fail.
Making exit_reason a 16-bit alias of the full/extended exit_reason neatly
sidesteps that issue. And it is an issue that has caused actual problems
in the past, e.g. see commit beb8d93b3e42 ("KVM: VMX: Fix handling of #MC
that occurs during VM-Entry"). Coincidentally, that commit also removes a
local "u16 basic_exit_reason" :-).
Except for one mistake, the pseudo-patch below is the entirety of required
changes. Most (all?) of the functions that take "u32 exit_reason" can (and
should) continue to take a u32.
As for the name, I strongly prefer keeping the exit_reason name for the
basic exit reason. The vast majority of VM-Exits do not have modifiers
set, i.e. "basic exit reason" == vmcs.EXIT_REASON for nearly all normal
usage. This holds true in every form of communication, e.g. when discussing
VM-Exit reasons, it's never qualified with "basic", it's simply the exit
reason. IMO the code is better off following the colloquial usage of "exit
reason". A simple comment above the union would suffice to clear up any
confusion with respect to the SDM.
Well, for this reason we can keep exit_reason for 16-bit usage, and
define full/extended_exit_reason for 32-bit cases. This makes less code
churn.
But after we choose to use exit_reason and full/extended_exit_reason,
what if someday new modifier flags are added and we want to enable some
modifier flags for nested case?
I guess we need to change existing exit_reason to
full/extended_exit_reason in nested.c/nested.h to keep the naming rule
consistent.
Maybe we name it
union {
u16 basic_exit_reason;
u32 exit_reason;
}
as what SDM defines?
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5818,7 +5818,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
if (is_guest_mode(vcpu) && nested_vmx_exit_reflected(vcpu, exit_reason))
return nested_vmx_reflect_vmexit(vcpu, exit_reason);
- if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
+ if (vmx->full_exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
If we do go the union route, this snippet of code is insufficient, the
full/extended exit reason needs to be snapshotted early for use in the
tracepoint and in fail_entry.hardware_entry_failure_reason.
dump_vmcs();
vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY;
vcpu->run->fail_entry.hardware_entry_failure_reason
@@ -6620,11 +6620,12 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
vmx->nested.nested_run_pending = 0;
vmx->idt_vectoring_info = 0;
- vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
- if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
+ vmx->full_exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
+ if (vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
kvm_machine_check();
- if (vmx->fail || (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
+ if (vmx->fail ||
+ (vmx->full_exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
return;
vmx->loaded_vmcs->launched = 1;
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 7f42cf3dcd70..60c09640ea59 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -260,7 +260,10 @@ struct vcpu_vmx {
int vpid;
bool emulation_required;
- u32 exit_reason;
+ union {
+ u16 exit_reason;
+ u32 full_exit_reason;
+ }
/* Posted interrupt descriptor */
struct pi_desc pi_desc;
--
Vitaly
