linux-kernel - Re: [PATCH] RISC-V: mm: Fix set_satp_mode() for platform not having Sv57

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Message-ID: <4c4c7a.17284.1802b8c14cc.Coremail.panqinglin2020@iscas.ac.cn>
Date:   Fri, 15 Apr 2022 12:47:22 +0800 (GMT+08:00)
From:   潘庆霖 <panqinglin2020@...as.ac.cn>
To:     "Anup Patel" <apatel@...tanamicro.com>
Cc:     "Palmer Dabbelt" <palmer@...belt.com>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        "Alexandre Ghiti" <alexandre.ghiti@...onical.com>,
        "Atish Patra" <atishp@...shpatra.org>,
        "Alistair Francis" <Alistair.Francis@....com>,
        "Anup Patel" <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Mayuresh Chitale" <mchitale@...tanamicro.com>
Subject: Re: [PATCH] RISC-V: mm: Fix set_satp_mode() for platform not having
 Sv57

Hi Anup,

&gt; 
&gt; When Sv57 is not available the satp.MODE test in set_satp_mode() will
&gt; fail and lead to pgdir re-programming for Sv48. The pgdir re-programming
&gt; will fail as well due to pre-existing pgdir entry used for Sv57 and as
&gt; a result kernel fails to boot on RISC-V platform not having Sv57.
&gt; 
&gt; To fix above issue, we should clear the pgdir memory in set_satp_mode()
&gt; before re-programming.
&gt; 
&gt; Fixes: 011f09d12052 ("riscv: mm: Set sv57 on defaultly")
&gt; Reported-by: Mayuresh Chitale <mchitale@...tanamicro.com>
&gt; Signed-off-by: Anup Patel <apatel@...tanamicro.com>
&gt; ---
&gt;  arch/riscv/mm/init.c | 1 +
&gt;  1 file changed, 1 insertion(+)
&gt; 
&gt; diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
&gt; index 9535bea8688c..b0793dc0c291 100644
&gt; --- a/arch/riscv/mm/init.c
&gt; +++ b/arch/riscv/mm/init.c
&gt; @@ -718,6 +718,7 @@ static __init void set_satp_mode(void)
&gt;  		if (!check_l4) {
&gt;  			disable_pgtable_l5();
&gt;  			check_l4 = true;
&gt; +			memset(early_pg_dir, 0, PAGE_SIZE);
&gt;  			goto retry;
&gt;  		}
&gt;  		disable_pgtable_l4();
&gt; -- 


I find it that the set_satp_mode function is in .init.text section which begins at 0x80800000.
And its pgd_index in both Sv48 and Sv57 will be 0. So it may not be necessary to clear the 
early_pg_dir when the kernel find Sv57 is not supported? And may I get the steps of reproduction
from you?
 
Yours,
Qinglin
</apatel@...tanamicro.com></mchitale@...tanamicro.com>