On 6/17/22 17:28, Sean Christopherson wrote:
On Mon, May 16, 2022, David Matlack wrote:
Allow @vcpu to be NULL in kvm_mmu_find_shadow_page() (and its only
caller __kvm_mmu_get_shadow_page()). @vcpu is only required to sync
indirect shadow pages, so it's safe to pass in NULL when looking up
direct shadow pages.
This will be used for doing eager page splitting, which allocates direct
"hugepage" again, because I need constant reminders :-)
shadow pages from the context of a VM ioctl without access to a vCPU
pointer.
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
---
With nits addressed,
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
arch/x86/kvm/mmu/mmu.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 4fbc2da47428..acb54d6e0ea5 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1850,6 +1850,7 @@ static int kvm_sync_page(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
if (ret < 0)
kvm_mmu_prepare_zap_page(vcpu->kvm, sp, invalid_list);
+
Unrelated whitespace change leftover from the previous approach.
return ret;
}
@@ -2001,6 +2002,7 @@ static void clear_sp_write_flooding_count(u64 *spte)
__clear_sp_write_flooding_count(sptep_to_sp(spte));
}
+/* Note, @vcpu may be NULL if @role.direct is true. */
static struct kvm_mmu_page *kvm_mmu_find_shadow_page(struct kvm *kvm,
struct kvm_vcpu *vcpu,
gfn_t gfn,
@@ -2039,6 +2041,16 @@ static struct kvm_mmu_page *kvm_mmu_find_shadow_page(struct kvm *kvm,
goto out;
if (sp->unsync) {
+ /*
+ * A vCPU pointer should always be provided when finding
s/should/must, and "be provided" in unnecessarily ambiguous, simply state that
"@vcpu must be non-NULL". E.g. if a caller provides a pointer, but that pointer
happens to be NULL.
+ * indirect shadow pages, as that shadow page may
+ * already exist and need to be synced using the vCPU
+ * pointer. Direct shadow pages are never unsync and
+ * thus do not require a vCPU pointer.
+ */
"vCPU pointer" over and over is a bit versbose, and I prefer to refer to vCPUs/VMs
as objects themselves. E.g. "XYZ requires a vCPU" versus "XYZ requires a vCPU
pointer" since it's not the pointer itself that's required, it's all the context
of the vCPU that is needed.
/*
* @vcpu must be non-NULL when finding indirect shadow
* pages, as such pages may already exist and need to
* be synced, which requires a vCPU. Direct pages are
* never unsync and thus do not require a vCPU.
*/
My own take:
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d7987420bb26..a7748c5a2385 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1975,7 +1975,12 @@ static void clear_sp_write_flooding_count(u64 *spte)
__clear_sp_write_flooding_count(sptep_to_sp(spte));
}
-/* Note, @vcpu may be NULL if @role.direct is true. */
+/*
+ * The vCPU is required when finding indirect shadow pages; the shadow
+ * page may already exist and syncing it needs the vCPU pointer in
+ * order to read guest page tables. Direct shadow pages are never
+ * unsync, thus @vcpu can be NULL if @role.direct is true.
+ */
static struct kvm_mmu_page *kvm_mmu_find_shadow_page(struct kvm *kvm,
struct kvm_vcpu *vcpu,
gfn_t gfn,
@@ -2014,13 +2019,6 @@ static struct kvm_mmu_page *kvm_mmu_find_shadow_page(struct kvm *kvm,
goto out;
if (sp->unsync) {
- /*
- * The vCPU pointer is required when finding indirect
- * shadow pages, as that shadow page may already exist
- * exist and need to be synced using the vCPU pointer.
- * Direct shadow pages are never unsync and thus do not
- * require a vCPU pointer.
- */
if (KVM_BUG_ON(!vcpu, kvm))
break;
@@ -2101,7 +2099,7 @@ static struct kvm_mmu_page *kvm_mmu_alloc_shadow_page(struct kvm *kvm,
return sp;
}
-/* Note, @vcpu may be NULL if @role.direct is true. */
+/* Note, @vcpu may be NULL if @role.direct is true; see kvm_mmu_find_shadow_page. */
static struct kvm_mmu_page *__kvm_mmu_get_shadow_page(struct kvm *kvm,
struct kvm_vcpu *vcpu,
struct shadow_page_caches *caches,
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