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Re: [RFC PATCH 2/2] accel/tcg: replace phys_pc with asid in TB htable ke

From: Richard Henderson
Subject: Re: [RFC PATCH 2/2] accel/tcg: replace phys_pc with asid in TB htable key
Date: Thu, 23 Dec 2021 08:31:21 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0

On 12/22/21 8:50 AM, Oleg Vasilev wrote:
From: Oleg Vasilev <vasilev.oleg@huawei.com>

Using a physical pc requires to translate address every time next block
needs to be found and executed. This also contaminates TLB with code-related

Instead, I suggest we introduce an architecture-specific address space
identifier, and use it to distinguish between different AS's
translation blocks.

Why do you believe that asid is sufficient here? You're not invalidating any more TBs that I can see. What happens when the kernel re-uses an asid?

I believe this patch to be fundamentally flawed.

All that said,

+/* Returns the identifier for a current address space. */
+static uint64_t arm_get_asid(CPUState *cs)
+    ARMCPU *cpu = ARM_CPU(cs);
+    CPUARMState *env = &cpu->env;
+    ARMMMUIdx mmu_idx = arm_mmu_idx(env);
+    uint64_t tcr = regime_tcr(env, mmu_idx)->raw_tcr;
+#define TCR_A1     (1U << 22)
+    return regime_ttbr(env, mmu_idx, (tcr&TCR_A1)>0);

Why are you returning the entire ttbr, and not the asid in the top 16 bits?


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