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Re: [PATCH] target/riscv: pmp: Fixup TLB size calculation

From: LIU Zhiwei
Subject: Re: [PATCH] target/riscv: pmp: Fixup TLB size calculation
Date: Wed, 12 Oct 2022 14:04:25 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.3.2

On 2022/10/12 11:09, Alistair Francis wrote:
On Wed, Oct 12, 2022 at 12:50 PM LIU Zhiwei
<zhiwei_liu@linux.alibaba.com> wrote:
Reviewed-by: LIU Zhiwei<zhiwei_liu@linux.alibaba.com>

By the way, we missed one related patch that once had been picked to riscv-next 

The patch v3:
So this was applied but caused boot failures so it was dropped from my
RISC-V tree

The patch v4:
I think I misunderstood this comment [1] as applying to v4 and it
never got applied.

Do you mind resending the patch?

Sure. I haveĀ  rebased it to your patch and sent it to the mail list.




I think the patch v4 should be taken at the same time with this patch.


On 2022/10/12 9:14, Alistair Francis wrote:
From: Alistair Francis <alistair.francis@wdc.com>

Since commit 4047368938f6 "accel/tcg: Introduce tlb_set_page_full" we
have been seeing this assert

      ../accel/tcg/cputlb.c:1294: tlb_set_page_with_attrs: Assertion 
`is_power_of_2(size)' failed.

When running Tock on the OpenTitan machine.

The issue is that pmp_get_tlb_size() would return a TLB size that wasn't
a power of 2. The size was also smaller then TARGET_PAGE_SIZE.

This patch ensures that any TLB size less then TARGET_PAGE_SIZE is
rounded down to 1 to ensure it's a valid size.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
This is based on advice from Richard:

   target/riscv/pmp.c | 12 ++++++++++++
   1 file changed, 12 insertions(+)

diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index ea2b67d947..2b43e399b8 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -628,6 +628,18 @@ bool pmp_is_range_in_tlb(CPURISCVState *env, hwaddr tlb_sa,

       if (*tlb_size != 0) {
+        /*
+         * At this point we have a tlb_size that is the smallest possible size
+         * That fits within a TARGET_PAGE_SIZE and the PMP region.
+         *
+         * If the size is less then TARGET_PAGE_SIZE we drop the size to 1.
+         * This means the result isn't cached in the TLB and is only used for
+         * a single translation.
+         */
+        if (*tlb_size < TARGET_PAGE_SIZE) {
+            *tlb_size = 1;
+        }
           return true;

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