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Subject[RFC V2 5/9] Modify the page fault path to meet the direct build EPT requirement
Date
From: Yulei Zhang <yulei.kernel@gmail.com>

Refine the fast page fault code so that it can be used in either
normal ept mode or direct build EPT mode.

Signed-off-by: Yulei Zhang <yuleixzhang@tencent.com>
---
arch/x86/kvm/mmu/mmu.c | 28 ++++++++++++++++++++--------
1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index f2124f52b286..fda6c4196854 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3443,12 +3443,13 @@ static bool page_fault_can_be_fast(u32 error_code)
* someone else modified the SPTE from its original value.
*/
static bool
-fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
+fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, gpa_t gpa,
u64 *sptep, u64 old_spte, u64 new_spte)
{
gfn_t gfn;

- WARN_ON(!sp->role.direct);
+ WARN_ON(!vcpu->arch.direct_build_tdp &&
+ (!sptep_to_sp(sptep)->role.direct));

/*
* Theoretically we could also set dirty bit (and flush TLB) here in
@@ -3470,7 +3471,8 @@ fast_pf_fix_direct_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
* The gfn of direct spte is stable since it is
* calculated by sp->gfn.
*/
- gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
+
+ gfn = gpa >> PAGE_SHIFT;
kvm_vcpu_mark_page_dirty(vcpu, gfn);
}

@@ -3498,10 +3500,10 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
u32 error_code)
{
struct kvm_shadow_walk_iterator iterator;
- struct kvm_mmu_page *sp;
bool fault_handled = false;
u64 spte = 0ull;
uint retry_count = 0;
+ int pte_level = 0;

if (!page_fault_can_be_fast(error_code))
return false;
@@ -3515,8 +3517,15 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
if (!is_shadow_present_pte(spte))
break;

- sp = sptep_to_sp(iterator.sptep);
- if (!is_last_spte(spte, sp->role.level))
+ if (iterator.level < PG_LEVEL_4K)
+ pte_level = PG_LEVEL_4K;
+ else
+ pte_level = iterator.level;
+
+ WARN_ON(!vcpu->arch.direct_build_tdp &&
+ (pte_level != sptep_to_sp(iterator.sptep)->role.level));
+
+ if (!is_last_spte(spte, pte_level))
break;

/*
@@ -3559,7 +3568,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
*
* See the comments in kvm_arch_commit_memory_region().
*/
- if (sp->role.level > PG_LEVEL_4K)
+ if (pte_level > PG_LEVEL_4K)
break;
}

@@ -3573,7 +3582,7 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
* since the gfn is not stable for indirect shadow page. See
* Documentation/virt/kvm/locking.rst to get more detail.
*/
- fault_handled = fast_pf_fix_direct_spte(vcpu, sp,
+ fault_handled = fast_pf_fix_direct_spte(vcpu, cr2_or_gpa,
iterator.sptep, spte,
new_spte);
if (fault_handled)
@@ -4106,6 +4115,9 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
if (fast_page_fault(vcpu, gpa, error_code))
return RET_PF_RETRY;

+ if (vcpu->arch.direct_build_tdp)
+ return RET_PF_EMULATE;
+
r = mmu_topup_memory_caches(vcpu, false);
if (r)
return r;
--
2.17.1
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