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Message-ID: <20230602160914.4011728-13-vipinsh@google.com>
Date: Fri, 2 Jun 2023 09:09:10 -0700
From: Vipin Sharma <vipinsh@...gle.com>
To: maz@...nel.org, oliver.upton@...ux.dev, james.morse@....com,
suzuki.poulose@....com, yuzenghui@...wei.com,
catalin.marinas@....com, will@...nel.org, chenhuacai@...nel.org,
aleksandar.qemu.devel@...il.com, tsbogend@...ha.franken.de,
anup@...infault.org, atishp@...shpatra.org,
paul.walmsley@...ive.com, palmer@...belt.com,
aou@...s.berkeley.edu, seanjc@...gle.com, pbonzini@...hat.com,
dmatlack@...gle.com, ricarkol@...gle.com
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
linux-mips@...r.kernel.org, kvm-riscv@...ts.infradead.org,
linux-riscv@...ts.infradead.org, linux-kselftest@...r.kernel.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Vipin Sharma <vipinsh@...gle.com>
Subject: [PATCH v2 12/16] KVM: arm64: Retry shared page table walks outside of
fault handler
For a shared page walker which is not fault handler, retry the walk if
walker callback function returns -EAGAIN, or continue to the next SPTE
if callback function return -ENOENT. Update the kvm_pgtable_walk
documentation.
For fault handler logic remains same, i.e. exit the walk and resume the
guest when getting -EAGAIN and -ENOENT errors from walker callback
function.
Currently, there is no page walker which is shared and not a fault
handler, but this will change in future patches when clear-dirty-log
walker will use MMU read lock and run via shared walker.
Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
arch/arm64/include/asm/kvm_pgtable.h | 23 ++++++++++-------
arch/arm64/kvm/hyp/pgtable.c | 38 +++++++++++++++++++++++-----
2 files changed, 46 insertions(+), 15 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 23e7e7851f1d..145be12a5fc2 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -716,15 +716,20 @@ int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
* type of the walker, i.e. shared walker (vCPU fault handlers) or non-shared
* walker.
*
- * Walker Type | Callback | Walker action
- * -------------|------------------|--------------
- * Non-Shared | 0 | Continue
- * Non-Shared | -EAGAIN | Continue
- * Non-Shared | -ENOENT | Continue
- * Non-Shared | Any other | Exit
- * -------------|------------------|--------------
- * Shared | 0 | Continue
- * Shared | Any other | Exit
+ * Walker Type | Callback | Walker action
+ * -----------------------|------------------|--------------
+ * Non-Shared | 0 | Continue
+ * Non-Shared | -EAGAIN | Continue
+ * Non-Shared | -ENOENT | Continue
+ * Non-Shared | Any other | Exit
+ * -----------------------|------------------|--------------
+ * Shared | 0 | Continue
+ * Shared | -EAGAIN | Retry
+ * Shared | -ENOENT | Continue
+ * Shared | Any other | Exit
+ * -----------------------|------------------|--------------
+ * Shared (Fault Handler) | 0 | Continue
+ * Shared (Fault Handler) | Any other | Exit
*
* Return: 0 on success, negative error code on failure.
*/
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 7f80e953b502..23cda3de2dd4 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -191,15 +191,21 @@ static bool kvm_pgtable_walk_continue(const struct kvm_pgtable_walker *walker,
* Callbacks can also return ENOENT when PTE which is visited is not
* valid.
*
- * In the context of a shared walker interpret these as a signal
+ * In the context of a fault handler interpret these as a signal
* to retry guest execution.
*
- * Ignore these return codes altogether for walkers outside a fault
- * handler (e.g. write protecting a range of memory) and chug along
+ * In the context of a shared walker which is not fault handler
+ * interpret:
+ * 1. EAGAIN - A signal to retry walk again.
+ * 2. ENOENT - A signal to ignore and move on to next SPTE.
+ *
+ * Ignore these return codes altogether for other walkers and chug along
* with the page table walk.
*/
- if (r == -EAGAIN || r == -ENOENT)
+ if (r == -EAGAIN)
return !(walker->flags & KVM_PGTABLE_WALK_SHARED);
+ if (r == -ENOENT)
+ return !(walker->flags & KVM_PGTABLE_WALK_HANDLE_FAULT);
return !r;
}
@@ -260,24 +266,44 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
return ret;
}
+static bool kvm_pgtable_walk_retry(const struct kvm_pgtable_walker *walker,
+ int r)
+{
+ /*
+ * All shared page table walks where visitor callbacks return -EAGAIN
+ * should be retried with the exception of fault handler. In case of
+ * fault handler retry is achieved by resuming the guest.
+ */
+ if (r == -EAGAIN)
+ return (walker->flags & KVM_PGTABLE_WALK_SHARED) &&
+ !(walker->flags & KVM_PGTABLE_WALK_HANDLE_FAULT);
+
+ return !r;
+}
+
static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, u32 level)
{
u32 idx;
int ret = 0;
+ kvm_pteref_t pteref;
if (WARN_ON_ONCE(level >= KVM_PGTABLE_MAX_LEVELS))
return -EINVAL;
for (idx = kvm_pgtable_idx(data, level); idx < PTRS_PER_PTE; ++idx) {
- kvm_pteref_t pteref = &pgtable[idx];
+retry:
+ pteref = &pgtable[idx];
if (data->addr >= data->end)
break;
ret = __kvm_pgtable_visit(data, mm_ops, pteref, level);
- if (ret)
+ if (ret) {
+ if (kvm_pgtable_walk_retry(data->walker, ret))
+ goto retry;
break;
+ }
}
return ret;
--
2.41.0.rc0.172.g3f132b7071-goog
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