On 2022/4/23 05:05, David Matlack wrote:
Instead of computing the shadow page role from scratch for every new
page, derive most of the information from the parent shadow page. This
avoids redundant calculations and reduces the number of parameters to
kvm_mmu_get_page().
Preemptively split out the role calculation to a separate function for
use in a following commit.
No functional change intended.
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 96 +++++++++++++++++++++++-----------
arch/x86/kvm/mmu/paging_tmpl.h | 9 ++--
2 files changed, 71 insertions(+), 34 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index dc20eccd6a77..4249a771818b 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2021,31 +2021,15 @@ static void clear_sp_write_flooding_count(u64 *spte)
__clear_sp_write_flooding_count(sptep_to_sp(spte));
}
-static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
- gfn_t gfn,
- gva_t gaddr,
- unsigned level,
- bool direct,
- unsigned int access)
+static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn,
+ union kvm_mmu_page_role role)
{
- union kvm_mmu_page_role role;
struct hlist_head *sp_list;
- unsigned quadrant;
struct kvm_mmu_page *sp;
int ret;
int collisions = 0;
LIST_HEAD(invalid_list);
- role = vcpu->arch.mmu->root_role;
- role.level = level;
- role.direct = direct;
- role.access = access;
- if (role.has_4_byte_gpte) {
- quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
- quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
- role.quadrant = quadrant;
- }
I don't think replacing it with kvm_mmu_child_role() can reduce any calculations.
role.level, role.direct, role.access and role.quadrant still need to be
calculated. And the old code is still in mmu_alloc_root().
I think kvm_mmu_get_shadow_page() can keep the those parameters and
kvm_mmu_child_role() is only introduced for nested_mmu_get_sp_for_split().
Both kvm_mmu_get_shadow_page() and nested_mmu_get_sp_for_split() call
__kvm_mmu_get_shadow_page() which uses role as a parameter.
-
sp_list = &vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)];
for_each_valid_sp(vcpu->kvm, sp, sp_list) {
if (sp->gfn != gfn) {
@@ -2063,7 +2047,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
* Unsync pages must not be left as is, because the new
* upper-level page will be write-protected.
*/
- if (level > PG_LEVEL_4K && sp->unsync)
+ if (role.level > PG_LEVEL_4K && sp->unsync)
kvm_mmu_prepare_zap_page(vcpu->kvm, sp,
&invalid_list);
continue;
@@ -2104,14 +2088,14 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
++vcpu->kvm->stat.mmu_cache_miss;
- sp = kvm_mmu_alloc_page(vcpu, direct);
+ sp = kvm_mmu_alloc_page(vcpu, role.direct);
sp->gfn = gfn;
sp->role = role;
hlist_add_head(&sp->hash_link, sp_list);
- if (!direct) {
+ if (!role.direct) {
account_shadowed(vcpu->kvm, sp);
- if (level == PG_LEVEL_4K && kvm_vcpu_write_protect_gfn(vcpu, gfn))
+ if (role.level == PG_LEVEL_4K && kvm_vcpu_write_protect_gfn(vcpu, gfn))
kvm_flush_remote_tlbs_with_address(vcpu->kvm, gfn, 1);
}
trace_kvm_mmu_get_page(sp, true);
@@ -2123,6 +2107,51 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
return sp;
}
+static union kvm_mmu_page_role kvm_mmu_child_role(u64 *sptep, bool direct, u32 access)
+{
+ struct kvm_mmu_page *parent_sp = sptep_to_sp(sptep);
+ union kvm_mmu_page_role role;
+
+ role = parent_sp->role;
+ role.level--;
+ role.access = access;
+ role.direct = direct;
+
+ /*
+ * If the guest has 4-byte PTEs then that means it's using 32-bit,
+ * 2-level, non-PAE paging. KVM shadows such guests using 4 PAE page
+ * directories, each mapping 1/4 of the guest's linear address space
+ * (1GiB). The shadow pages for those 4 page directories are
+ * pre-allocated and assigned a separate quadrant in their role.
It is not going to be true in patchset:
[PATCH V2 0/7] KVM: X86/MMU: Use one-off special shadow page for special roots
https://lore.kernel.org/lkml/20220503150735.32723-1-jiangshanlai@xxxxxxxxx/
The shadow pages for those 4 page directories are also allocated on demand.
