Re: [PATCH 1/2] kfence: allow providing __kfence_pool in arch specific way

On Mon, 24 May 2021 12:36:34 +0200
Marco Elver [off-list ref] wrote:

On Mon, 24 May 2021 at 11:26, Jisheng Zhang [off-list ref] wrote:

quoted

Some architectures may want to allocate the __kfence_pool differently
for example, allocate the __kfence_pool earlier before paging_init().
We also delay the memset() to kfence_init_pool().

Signed-off-by: Jisheng Zhang <redacted>
---
 mm/kfence/core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index e18fbbd5d9b4..65f0210edb65 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c

@@ -430,6 +430,8 @@ static bool __init kfence_init_pool(void)
        if (!__kfence_pool)
                return false;

+       memset(__kfence_pool, 0, KFENCE_POOL_SIZE);
+  

Use memzero_explicit().

Also, for the arm64 case, is delaying the zeroing relevant? You still
call kfence_alloc_pool() in patch 2/2, and zeroing it on
memblock_alloc() is not wrong, correct?

memblock_alloc() returns virtual address which can't be used before paging_init()
so I delayed the memset to kfence_init_pool.

Essentially if there's not going to be any benefit to us doing the
zeroing ourselves, I'd simply leave it as-is and keep using
memblock_alloc(). And if there's some odd architecture that doesn't
even want to use kfence_alloc_pool(), they could just zero the memory
themselves. But we really should use kfence_alloc_pool(), because
otherwise it'll just become unmaintainable if on changes to
kfence_alloc_pool() we have to go and find other special architectures
that don't use it and adjust them, too.

Thanks,
-- Marco

quoted

        if (!arch_kfence_init_pool())
                goto err;

@@ -645,10 +647,10 @@ static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate);

 void __init kfence_alloc_pool(void)
 {
-       if (!kfence_sample_interval)
+       if (!kfence_sample_interval || __kfence_pool)
                return;

-       __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+       __kfence_pool = memblock_alloc_raw(KFENCE_POOL_SIZE, PAGE_SIZE);

        if (!__kfence_pool)
                pr_err("failed to allocate pool\n");
--

2.31.0
 

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