Rework the function comment for kvm_arch_mmu_enable_log_dirty_pt_masked()
into the body of the function, as it has gotten a bit stale, is harder to
read without the code context, and is the last source of warnings for W=1
builds in KVM x86 due to using a kernel-doc comment without documenting
all parameters.
Opportunistically subsume the functions comments for
kvm_mmu_write_protect_pt_masked() and kvm_mmu_clear_dirty_pt_masked(), as
there is no value in regurgitating similar information at a higher level,
and capturing the differences between write-protection and PML-based dirty
logging is best done in a common location.
No functional change intended.
Cc: David Matlack <dmatlack@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
v2: Put the comments in the function body. [David]
v1: https://lore.kernel.org/all/20240611215805.340664-1-seanjc@xxxxxxxxxx
arch/x86/kvm/mmu/mmu.c | 48 +++++++++++++-----------------------------
1 file changed, 15 insertions(+), 33 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 901be9e420a4..45e7e9bd5e76 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1307,15 +1307,6 @@ static bool __rmap_clear_dirty(struct kvm *kvm, struct kvm_rmap_head *rmap_head,
return flush;
}
-/**
- * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages
- * @kvm: kvm instance
- * @slot: slot to protect
- * @gfn_offset: start of the BITS_PER_LONG pages we care about
- * @mask: indicates which pages we should protect
- *
- * Used when we do not need to care about huge page mappings.
- */
static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
gfn_t gfn_offset, unsigned long mask)
@@ -1339,16 +1330,6 @@ static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
}
}
-/**
- * kvm_mmu_clear_dirty_pt_masked - clear MMU D-bit for PT level pages, or write
- * protect the page if the D-bit isn't supported.
- * @kvm: kvm instance
- * @slot: slot to clear D-bit
- * @gfn_offset: start of the BITS_PER_LONG pages we care about
- * @mask: indicates which pages we should clear D-bit
- *
- * Used for PML to re-log the dirty GPAs after userspace querying dirty_bitmap.
- */
static void kvm_mmu_clear_dirty_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
gfn_t gfn_offset, unsigned long mask)
@@ -1372,24 +1353,16 @@ static void kvm_mmu_clear_dirty_pt_masked(struct kvm *kvm,
}
}
-/**
- * kvm_arch_mmu_enable_log_dirty_pt_masked - enable dirty logging for selected
- * PT level pages.
- *
- * It calls kvm_mmu_write_protect_pt_masked to write protect selected pages to
- * enable dirty logging for them.
- *
- * We need to care about huge page mappings: e.g. during dirty logging we may
- * have such mappings.
- */
void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
struct kvm_memory_slot *slot,
gfn_t gfn_offset, unsigned long mask)
{
/*
- * Huge pages are NOT write protected when we start dirty logging in
- * initially-all-set mode; must write protect them here so that they
- * are split to 4K on the first write.
+ * If the slot was assumed to be "initially all dirty", write-protect
+ * huge pages to ensure they are split to 4KiB on the first write (KVM
+ * dirty logs at 4KiB granularity). If eager page splitting is enabled,
+ * immediately try to split huge pages, e.g. so that vCPUs don't get
+ * saddled with the cost of splitting.
*
* The gfn_offset is guaranteed to be aligned to 64, but the base_gfn
* of memslot has no such restriction, so the range can cross two large
@@ -1411,7 +1384,16 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
PG_LEVEL_2M);
}
- /* Now handle 4K PTEs. */
+ /*
+ * (Re)Enable dirty logging for all 4KiB SPTEs that map the GFNs in
+ * mask. If PML is enabled and the and the GFN doesn't need to be
+ * write-protected for other reasons, e.g. shadow paging, clear the
+ * Dirty bit. Otherwise clear the Writable bit.
+ *
+ * Note that kvm_mmu_clear_dirty_pt_masked() is called whenever PML is
+ * enabled but it chooses between clearing the Dirty bit and Writeable
+ * bit based on the context.
+ */
if (kvm_x86_ops.cpu_dirty_log_size)
kvm_mmu_clear_dirty_pt_masked(kvm, slot, gfn_offset, mask);
else
