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KVM: TDX: Fold tdx_mem_page_record_premap_cnt() into its sole caller

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Fold tdx_mem_page_record_premap_cnt() into tdx_sept_set_private_spte() as
providing a one-off helper for effectively three lines of code is at best a
wash, and splitting the code makes the comment for smp_rmb()  _extremely_
confusing as the comment talks about reading kvm->arch.pre_fault_allowed
before kvm_tdx->state, but the immediately visible code does the exact
opposite.

Opportunistically rewrite the comments to more explicitly explain who is
checking what, as well as _why_ the ordering matters.

No functional change intended.

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-16-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-10-30 13:09:38 -07:00
parent af96d5452e
commit b4b2b6eda5
1 changed files with 21 additions and 28 deletions
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49
arch/x86/kvm/vmx/tdx.c
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@ -1605,29 +1605,6 @@ static int tdx_mem_page_aug(struct kvm *kvm, gfn_t gfn,
return 0;
}
/*
* KVM_TDX_INIT_MEM_REGION calls kvm_gmem_populate() to map guest pages; the
* callback tdx_gmem_post_populate() then maps pages into private memory.
* through the a seamcall TDH.MEM.PAGE.ADD(). The SEAMCALL also requires the
* private EPT structures for the page to have been built before, which is
* done via kvm_tdp_map_page(). nr_premapped counts the number of pages that
* were added to the EPT structures but not added with TDH.MEM.PAGE.ADD().
* The counter has to be zero on KVM_TDX_FINALIZE_VM, to ensure that there
* are no half-initialized shared EPT pages.
*/
static int tdx_mem_page_record_premap_cnt(struct kvm *kvm, gfn_t gfn,
enum pg_level level, kvm_pfn_t pfn)
{
struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
if (KVM_BUG_ON(kvm->arch.pre_fault_allowed, kvm))
return -EIO;
/* nr_premapped will be decreased when tdh_mem_page_add() is called. */
atomic64_inc(&kvm_tdx->nr_premapped);
return 0;
}
static int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
enum pg_level level, u64 mirror_spte)
{
@ -1642,14 +1619,30 @@ static int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn,
(mirror_spte & VMX_EPT_RWX_MASK) != VMX_EPT_RWX_MASK);
/*
* Read 'pre_fault_allowed' before 'kvm_tdx->state'; see matching
* barrier in tdx_td_finalize().
* Ensure pre_fault_allowed is read by kvm_arch_vcpu_pre_fault_memory()
* before kvm_tdx->state. Userspace must not be allowed to pre-fault
* arbitrary memory until the initial memory image is finalized. Pairs
* with the smp_wmb() in tdx_td_finalize().
*/
smp_rmb();
if (likely(kvm_tdx->state == TD_STATE_RUNNABLE))
return tdx_mem_page_aug(kvm, gfn, level, pfn);
return tdx_mem_page_record_premap_cnt(kvm, gfn, level, pfn);
/*
* If the TD isn't finalized/runnable, then userspace is initializing
* the VM image via KVM_TDX_INIT_MEM_REGION. Increment the number of
* pages that need to be mapped and initialized via TDH.MEM.PAGE.ADD.
* KVM_TDX_FINALIZE_VM checks the counter to ensure all pre-mapped
* pages have been added to the image, to prevent running the TD with a
* valid mapping in the mirror EPT, but not in the S-EPT.
*/
if (unlikely(kvm_tdx->state != TD_STATE_RUNNABLE)) {
if (KVM_BUG_ON(kvm->arch.pre_fault_allowed, kvm))
return -EIO;
atomic64_inc(&kvm_tdx->nr_premapped);
return 0;
}
return tdx_mem_page_aug(kvm, gfn, level, pfn);
}
static int tdx_sept_link_private_spt(struct kvm *kvm, gfn_t gfn,