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KVM: Drop extra GUP (via check_user_page_hwpoison()) to detect poisoned page

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Remove check_user_page_hwpoison() as it's effectively dead code.  Prior to
commit 234b239bea ("kvm: Faults which trigger IO release the mmap_sem"),
hva_to_pfn_slow() wasn't actually a slow path in all cases, i.e. would do
get_user_pages_fast() without ever doing slow GUP with FOLL_HWPOISON.

Now that hva_to_pfn_slow() is a straight shot to get_user_pages_unlocked(),
and unconditionally passes FOLL_HWPOISON, it is impossible for hva_to_pfn()
to get an -errno that needs to be morphed to -EHWPOISON.

There are essentially four cases in KVM:

  - npages == 0, then FOLL_NOWAIT, a.k.a. @async, must be true, and thus
    check_user_page_hwpoison() will not be called
  - npages == 1 || npages == -EHWPOISON, all good
  - npages == -EINTR || npages == -EAGAIN, bail early, all good
  - everything else, including -EFAULT, can go down the vma_lookup() path,
    as npages < 0 means KVM went through hva_to_pfn_slow() which passes
    FOLL_HWPOISON

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-16-seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-10-10 11:23:17 -07:00 committed by Paolo Bonzini
parent d1331a4469
commit b176f4b417
1 changed files with 2 additions and 15 deletions
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17
virt/kvm/kvm_main.c
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@ -2746,14 +2746,6 @@ unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *w
return gfn_to_hva_memslot_prot(slot, gfn, writable);
}
static inline int check_user_page_hwpoison(unsigned long addr)
{
int rc, flags = FOLL_HWPOISON | FOLL_WRITE;
rc = get_user_pages(addr, 1, flags, NULL);
return rc == -EHWPOISON;
}
/*
* The fast path to get the writable pfn which will be stored in @pfn,
* true indicates success, otherwise false is returned.
@ -2948,14 +2940,10 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool interruptible, bool *async,
return pfn;
if (npages == -EINTR || npages == -EAGAIN)
return KVM_PFN_ERR_SIGPENDING;
if (npages == -EHWPOISON)
return KVM_PFN_ERR_HWPOISON;
mmap_read_lock(current->mm);
if (npages == -EHWPOISON ||
(!async && check_user_page_hwpoison(addr))) {
pfn = KVM_PFN_ERR_HWPOISON;
goto exit;
}
retry:
vma = vma_lookup(current->mm, addr);
@ -2972,7 +2960,6 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool interruptible, bool *async,
*async = true;
pfn = KVM_PFN_ERR_FAULT;
}
exit:
mmap_read_unlock(current->mm);
return pfn;
}