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KVM: Allow cross page reads and writes from cached translations.

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This patch adds support for kvm_gfn_to_hva_cache_init functions for
reads and writes that will cross a page.  If the range falls within
the same memslot, then this will be a fast operation.  If the range
is split between two memslots, then the slower kvm_read_guest and
kvm_write_guest are used.

Tested: Test against kvm_clock unit tests.

Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
This commit is contained in:
Andrew Honig
2013-03-29 09:35:21 -07:00
committed by Gleb Natapov
parent 09a6e1f4ad
commit 8f964525a1
5 changed files with 46 additions and 19 deletions
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47
virt/kvm/kvm_main.c
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@@ -1541,21 +1541,38 @@ int kvm_write_guest(struct kvm *kvm, gpa_t gpa, const void *data,
}
int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
gpa_t gpa)
gpa_t gpa, unsigned long len)
{
struct kvm_memslots *slots = kvm_memslots(kvm);
int offset = offset_in_page(gpa);
gfn_t gfn = gpa >> PAGE_SHIFT;
gfn_t start_gfn = gpa >> PAGE_SHIFT;
gfn_t end_gfn = (gpa + len - 1) >> PAGE_SHIFT;
gfn_t nr_pages_needed = end_gfn - start_gfn + 1;
gfn_t nr_pages_avail;
ghc->gpa = gpa;
ghc->generation = slots->generation;
ghc->memslot = gfn_to_memslot(kvm, gfn);
ghc->hva = gfn_to_hva_many(ghc->memslot, gfn, NULL);
if (!kvm_is_error_hva(ghc->hva))
ghc->len = len;
ghc->memslot = gfn_to_memslot(kvm, start_gfn);
ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn, &nr_pages_avail);
if (!kvm_is_error_hva(ghc->hva) && nr_pages_avail >= nr_pages_needed) {
ghc->hva += offset;
else
return -EFAULT;
} else {
/*
* If the requested region crosses two memslots, we still
* verify that the entire region is valid here.
*/
while (start_gfn <= end_gfn) {
ghc->memslot = gfn_to_memslot(kvm, start_gfn);
ghc->hva = gfn_to_hva_many(ghc->memslot, start_gfn,
&nr_pages_avail);
if (kvm_is_error_hva(ghc->hva))
return -EFAULT;
start_gfn += nr_pages_avail;
}
/* Use the slow path for cross page reads and writes. */
ghc->memslot = NULL;
}
return 0;
}
EXPORT_SYMBOL_GPL(kvm_gfn_to_hva_cache_init);
@@ -1566,8 +1583,13 @@ int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
struct kvm_memslots *slots = kvm_memslots(kvm);
int r;
BUG_ON(len > ghc->len);
if (slots->generation != ghc->generation)
kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa);
kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa, ghc->len);
if (unlikely(!ghc->memslot))
return kvm_write_guest(kvm, ghc->gpa, data, len);
if (kvm_is_error_hva(ghc->hva))
return -EFAULT;
@@ -1587,8 +1609,13 @@ int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
struct kvm_memslots *slots = kvm_memslots(kvm);
int r;
BUG_ON(len > ghc->len);
if (slots->generation != ghc->generation)
kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa);
kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa, ghc->len);
if (unlikely(!ghc->memslot))
return kvm_read_guest(kvm, ghc->gpa, data, len);
if (kvm_is_error_hva(ghc->hva))
return -EFAULT;