From: Sean Christopherson <seanjc@google.com>
To: David Matlack <dmatlack@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>,
Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH 00/23] KVM: MMU: MMU role refactoring
Date: Thu, 10 Feb 2022 01:11:56 +0000 [thread overview]
Message-ID: <YgRmXDn7b8GQ+VzX@google.com> (raw)
In-Reply-To: <CALzav=d05sMd=ARkV+GMf9SkxKcg9c9n5ttb274M2fZrP27PDA@mail.gmail.com>
On Mon, Feb 07, 2022, David Matlack wrote:
> On Mon, Feb 7, 2022 at 3:27 PM Sean Christopherson <seanjc@google.com> wrote:
> > > What do you think about calling this the guest_role instead of cpu_role?
> > > There is a bit of a precedent for using "guest" instead of "cpu" already
> > > for this type of concept (e.g. guest_walker), and I find it more
> > > intuitive.
> >
> > Haven't looked at the series yet, but I'd prefer not to use guest_role, it's
> > too similar to is_guest_mode() and kvm_mmu_role.guest_mode. E.g. we'd end up with
> >
> > static union kvm_mmu_role kvm_calc_guest_role(struct kvm_vcpu *vcpu,
> > const struct kvm_mmu_role_regs *regs)
> > {
> > union kvm_mmu_role role = {0};
> >
> > role.base.access = ACC_ALL;
> > role.base.smm = is_smm(vcpu);
> > role.base.guest_mode = is_guest_mode(vcpu);
> > role.base.direct = !____is_cr0_pg(regs);
> >
> > ...
> > }
> >
> > and possibly
> >
> > if (guest_role.guest_mode)
> > ...
> >
> > which would be quite messy. Maybe vcpu_role if cpu_role isn't intuitive?
>
> I agree it's a little odd. But actually it's somewhat intuitive (the
> guest is in guest-mode, i.e. we're running a nested guest).
>
> Ok I'm stretching a little bit :). But if the trade-off is just
> "guest_role.guest_mode" requires a clarifying comment, but the rest of
> the code gets more readable (cpu_role is used a lot more than
> role.guest_mode), it still might be worth it.
It's not just guest_mode, we also have guest_mmu, e.g. we'd end up with
vcpu->arch.root_mmu.guest_role.base.level
vcpu->arch.guest_mmu.guest_role.base.level
vcpu->arch.nested_mmu.guest_role.base.level
In a vacuum, I 100% agree that guest_role is better than cpu_role or vcpu_role,
but the term "guest" has already been claimed for "L2" in far too many places.
While we're behind the bikeshed... the resulting:
union kvm_mmu_role cpu_role;
union kvm_mmu_page_role mmu_role;
is a mess. Again, I really like "mmu_role" in a vacuum, but juxtaposed with
union kvm_mmu_role cpu_role;
it's super confusing, e.g. I expected
union kvm_mmu_role mmu_role;
Nested EPT is a good example of complete confusion, because we compute kvm_mmu_role,
compare it to cpu_role, then shove it into both cpu_role and mmu_ole. It makes
sense once you reason about what it's doing, but on the surface it's confusing.
struct kvm_mmu *context = &vcpu->arch.guest_mmu;
u8 level = vmx_eptp_page_walk_level(new_eptp);
union kvm_mmu_role new_role =
kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty,
execonly, level);
if (new_role.as_u64 != context->cpu_role.as_u64) {
/* EPT, and thus nested EPT, does not consume CR0, CR4, nor EFER. */
context->cpu_role.as_u64 = new_role.as_u64;
context->mmu_role.word = new_role.base.word;
Mabye this?
union kvm_mmu_vcpu_role vcpu_role;
union kvm_mmu_page_role mmu_role;
and some sample usage?
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d25f8cb2e62b..9f9b97c88738 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4836,13 +4836,16 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
{
struct kvm_mmu *context = &vcpu->arch.guest_mmu;
u8 level = vmx_eptp_page_walk_level(new_eptp);
- union kvm_mmu_role new_role =
+ union kvm_mmu_vcpu_role new_role =
kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty,
execonly, level);
- if (new_role.as_u64 != context->cpu_role.as_u64) {
- /* EPT, and thus nested EPT, does not consume CR0, CR4, nor EFER. */
- context->cpu_role.as_u64 = new_role.as_u64;
+ if (new_role.as_u64 != context->vcpu_role.as_u64) {
+ /*
+ * EPT, and thus nested EPT, does not consume CR0, CR4, nor
+ * EFER, so the mmu_role is a strict subset of the vcpu_role.
+ */
+ context->vcpu_role.as_u64 = new_role.as_u64;
context->mmu_role.word = new_role.base.word;
context->page_fault = ept_page_fault;
And while I'm on a soapbox.... am I the only one that absolutely detests the use
of "context" and "g_context"? I'd be all in favor of renaming those to "mmu"
throughout the code as a prep to this series.
I also think we should move the initializing of guest_mmu => mmu into the MMU
helpers. Pulling the mmu from guest_mmu but then relying on the caller to wire
up guest_mmu => mmu so that e.g. kvm_mmu_new_pgd() works is gross and confused
the heck out of me. E.g.
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d25f8cb2e62b..4e7fe9758ce8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4794,7 +4794,7 @@ static void kvm_init_shadow_mmu(struct kvm_vcpu *vcpu,
void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
unsigned long cr4, u64 efer, gpa_t nested_cr3)
{
- struct kvm_mmu *context = &vcpu->arch.guest_mmu;
+ struct kvm_mmu *mmu = &vcpu->arch.guest_mmu;
struct kvm_mmu_role_regs regs = {
.cr0 = cr0,
.cr4 = cr4 & ~X86_CR4_PKE,
@@ -4806,6 +4806,8 @@ void kvm_init_shadow_npt_mmu(struct kvm_vcpu *vcpu, unsigned long cr0,
mmu_role = cpu_role.base;
mmu_role.level = kvm_mmu_get_tdp_level(vcpu);
+ vcpu->arch.mmu = &vcpu->arch.guest_mmu;
+
shadow_mmu_init_context(vcpu, context, cpu_role, mmu_role);
kvm_mmu_new_pgd(vcpu, nested_cr3);
}
@@ -4834,12 +4836,14 @@ void kvm_init_shadow_ept_mmu(struct kvm_vcpu *vcpu, bool execonly,
int huge_page_level, bool accessed_dirty,
gpa_t new_eptp)
{
- struct kvm_mmu *context = &vcpu->arch.guest_mmu;
+ struct kvm_mmu *mmu = &vcpu->arch.guest_mmu;
u8 level = vmx_eptp_page_walk_level(new_eptp);
union kvm_mmu_role new_role =
kvm_calc_shadow_ept_root_page_role(vcpu, accessed_dirty,
execonly, level);
+ vcpu->arch.mmu = mmu;
+
if (new_role.as_u64 != context->cpu_role.as_u64) {
/* EPT, and thus nested EPT, does not consume CR0, CR4, nor EFER. */
context->cpu_role.as_u64 = new_role.as_u64;
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 1218b5a342fc..d0f8eddb32be 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -98,8 +98,6 @@ static void nested_svm_init_mmu_context(struct kvm_vcpu *vcpu)
WARN_ON(mmu_is_nested(vcpu));
- vcpu->arch.mmu = &vcpu->arch.guest_mmu;
-
/*
* The NPT format depends on L1's CR4 and EFER, which is in vmcb01. Note,
* when called via KVM_SET_NESTED_STATE, that state may _not_ match current
next prev parent reply other threads:[~2022-02-10 1:57 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 11:56 [PATCH 00/23] KVM: MMU: MMU role refactoring Paolo Bonzini
2022-02-04 11:56 ` [PATCH 01/23] KVM: MMU: pass uses_nx directly to reset_shadow_zero_bits_mask Paolo Bonzini
2022-02-04 17:59 ` David Matlack
2022-02-05 14:52 ` Paolo Bonzini
2022-02-07 16:09 ` Sean Christopherson
2022-02-07 21:50 ` David Matlack
2022-02-10 0:30 ` Sean Christopherson
2022-02-10 16:38 ` Paolo Bonzini
2022-02-04 11:56 ` [PATCH 02/23] KVM: MMU: nested EPT cannot be used in SMM Paolo Bonzini
2022-02-04 18:16 ` David Matlack
2022-02-09 22:43 ` Sean Christopherson
2022-02-04 11:56 ` [PATCH 03/23] KVM: MMU: remove valid from extended role Paolo Bonzini
2022-02-04 18:32 ` David Matlack
2022-02-05 14:50 ` Paolo Bonzini
2022-02-09 22:54 ` Sean Christopherson
2022-02-10 9:53 ` Paolo Bonzini
2022-02-04 11:56 ` [PATCH 04/23] KVM: MMU: constify uses of struct kvm_mmu_role_regs Paolo Bonzini
2022-02-04 18:41 ` David Matlack
2022-02-09 22:57 ` Sean Christopherson
2022-02-04 11:57 ` [PATCH 05/23] KVM: MMU: pull computation of kvm_mmu_role_regs to kvm_init_mmu Paolo Bonzini
2022-02-04 18:45 ` David Matlack
2022-02-04 11:57 ` [PATCH 06/23] KVM: MMU: load new PGD once nested two-dimensional paging is initialized Paolo Bonzini
2022-02-04 19:18 ` David Matlack
2022-02-07 13:50 ` Paolo Bonzini
2022-02-07 14:35 ` Paolo Bonzini
2022-02-09 12:34 ` Paolo Bonzini
2022-02-04 11:57 ` [PATCH 07/23] KVM: MMU: remove kvm_mmu_calc_root_page_role Paolo Bonzini
2022-02-04 19:32 ` David Matlack
2022-02-05 14:46 ` Paolo Bonzini
2022-02-10 0:47 ` Sean Christopherson
2022-02-10 9:52 ` Paolo Bonzini
2022-02-10 17:29 ` Sean Christopherson
2022-02-10 17:43 ` Paolo Bonzini
2022-02-04 11:57 ` [PATCH 08/23] KVM: MMU: rephrase unclear comment Paolo Bonzini
2022-02-04 19:38 ` David Matlack
2022-02-04 11:57 ` [PATCH 09/23] KVM: MMU: remove "bool base_only" arguments Paolo Bonzini
2022-02-04 19:41 ` David Matlack
2022-02-04 11:57 ` [PATCH 10/23] KVM: MMU: split cpu_role from mmu_role Paolo Bonzini
2022-02-04 21:57 ` David Matlack
2022-02-05 14:49 ` Paolo Bonzini
2022-02-07 21:38 ` David Matlack
2022-02-04 11:57 ` [PATCH 11/23] KVM: MMU: do not recompute root level from kvm_mmu_role_regs Paolo Bonzini
2022-02-07 22:10 ` David Matlack
2022-02-07 22:17 ` David Matlack
2022-02-04 11:57 ` [PATCH 12/23] KVM: MMU: remove ept_ad field Paolo Bonzini
2022-02-04 11:57 ` [PATCH 13/23] KVM: MMU: remove kvm_calc_shadow_root_page_role_common Paolo Bonzini
2022-02-07 22:25 ` David Matlack
2022-02-04 11:57 ` [PATCH 14/23] KVM: MMU: cleanup computation of MMU roles for two-dimensional paging Paolo Bonzini
2022-02-04 11:57 ` [PATCH 15/23] KVM: MMU: cleanup computation of MMU roles for shadow paging Paolo Bonzini
2022-02-04 11:57 ` [PATCH 16/23] KVM: MMU: remove extended bits from mmu_role Paolo Bonzini
2022-02-04 11:57 ` [PATCH 17/23] KVM: MMU: remove redundant bits from extended role Paolo Bonzini
2022-02-04 11:57 ` [PATCH 18/23] KVM: MMU: fetch shadow EFER.NX from MMU role Paolo Bonzini
2022-02-04 11:57 ` [PATCH 19/23] KVM: MMU: simplify and/or inline computation of shadow MMU roles Paolo Bonzini
2022-02-04 11:57 ` [PATCH 20/23] KVM: MMU: pull CPU role computation to kvm_init_mmu Paolo Bonzini
2022-02-07 22:42 ` David Matlack
2022-02-04 11:57 ` [PATCH 21/23] KVM: MMU: store shadow_root_level into mmu_role Paolo Bonzini
2022-02-07 23:00 ` David Matlack
2022-02-04 11:57 ` [PATCH 22/23] KVM: MMU: use cpu_role for root_level Paolo Bonzini
2022-02-07 23:01 ` David Matlack
2022-02-04 11:57 ` [PATCH 23/23] KVM: MMU: replace direct_map with mmu_role.direct Paolo Bonzini
2022-02-07 23:02 ` David Matlack
2022-02-07 23:08 ` [PATCH 00/23] KVM: MMU: MMU role refactoring David Matlack
2022-02-07 23:27 ` Sean Christopherson
2022-02-07 23:53 ` David Matlack
2022-02-10 1:11 ` Sean Christopherson [this message]
2022-02-10 11:58 ` Paolo Bonzini
2022-02-10 16:55 ` Sean Christopherson
2022-02-10 17:30 ` Paolo Bonzini
2022-02-10 19:28 ` Sean Christopherson
2022-02-09 22:31 ` Sean Christopherson
2022-02-10 9:54 ` Paolo Bonzini
2022-02-14 18:14 ` David Matlack
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