Hi,
On 16/06/2020 10:35, Keqian Zhu wrote:
kvm_set_pte is called to replace a target PTE with a desired one.
We always do this without changing the desired one, but if dirty
status set by hardware is coverred, let caller know it.
Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
---
arch/arm64/kvm/mmu.c | 36 +++++++++++++++++++++++++++++++++++-
1 file changed, 35 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 5ad87bce23c0..27407153121b 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -194,11 +194,45 @@ static void clear_stage2_pmd_entry(struct kvm *kvm, pmd_t *pmd, phys_addr_t addr
put_page(virt_to_page(pmd));
}
-static inline void kvm_set_pte(pte_t *ptep, pte_t new_pte)
+#ifdef CONFIG_ARM64_HW_AFDBM
+/**
+ * @ret: true if dirty status set by hardware is coverred.
NIT: s/coverred/covered/, this is in several places.
+ */
+static bool kvm_set_pte(pte_t *ptep, pte_t new_pte)
+{
+ pteval_t old_pteval, new_pteval, pteval;
+ bool old_logging, new_no_write;
+
+ old_logging = kvm_hw_dbm_enabled() && !pte_none(*ptep) &&
+ kvm_s2pte_dbm(ptep);
+ new_no_write = pte_none(new_pte) || kvm_s2pte_readonly(&new_pte);
+
+ if (!old_logging || !new_no_write) {
+ WRITE_ONCE(*ptep, new_pte);
+ dsb(ishst);
+ return false;
+ }
+
+ new_pteval = pte_val(new_pte);
+ pteval = READ_ONCE(pte_val(*ptep));
This usage of *ptep looks wrong - it's read twice using READ_ONCE (once
in kvm_s2pte_dbm()) and once without any decoration (in the pte_none()
call). Which looks a bit dodgy and at the very least needs some
justification. AFAICT you would be better taking a local copy and using
that rather than reading from memory repeatedly.
+ do {
+ old_pteval = pteval;
+ pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, new_pteval);
+ } while (pteval != old_pteval);
This look appears to be reinventing xchg_relaxed(). Any reason we can't
just use xchg_relaxed()? Also we had a dsb() after the WRITE_ONCE but
you are using the _relaxed variant here. What is the justification for
not having a barrier?
+
+ return !kvm_s2pte_readonly(&__pte(pteval));
+}
+#else
+/**
+ * @ret: true if dirty status set by hardware is coverred.
+ */
+static inline bool kvm_set_pte(pte_t *ptep, pte_t new_pte)
{
WRITE_ONCE(*ptep, new_pte);
dsb(ishst);
+ return false;
}
+#endif /* CONFIG_ARM64_HW_AFDBM */
You might be able to avoid this #ifdef by redefining old_logging as:
old_logging = IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && ...
I *think* the compiler should be able to kill the dead code and leave
you with just the above when the config symbol is off.
Steve
static inline void kvm_set_pmd(pmd_t *pmdp, pmd_t new_pmd)
{
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