linux-kernel - [PATCH 5.17 010/219] RISC-V: KVM: Dont clear hgatp CSR in kvm_arch_vcpu

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Message-Id: <20220418121203.767117836@linuxfoundation.org>
Date:   Mon, 18 Apr 2022 14:09:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Anup Patel <apatel@...tanamicro.com>,
        Anup Patel <anup@...infault.org>
Subject: [PATCH 5.17 010/219] RISC-V: KVM: Dont clear hgatp CSR in kvm_arch_vcpu_put()

From: Anup Patel <apatel@...tanamicro.com>

commit 8c3ce496bd612bd21679e445f75fcabb6be997b2 upstream.

We might have RISC-V systems (such as QEMU) where VMID is not part
of the TLB entry tag so these systems will have to flush all TLB
entries upon any change in hgatp.VMID.

Currently, we zero-out hgatp CSR in kvm_arch_vcpu_put() and we
re-program hgatp CSR in kvm_arch_vcpu_load(). For above described
systems, this will flush all TLB entries whenever VCPU exits to
user-space hence reducing performance.

This patch fixes above described performance issue by not clearing
hgatp CSR in kvm_arch_vcpu_put().

Fixes: 34bde9d8b9e6 ("RISC-V: KVM: Implement VCPU world-switch")
Cc: stable@...r.kernel.org
Signed-off-by: Anup Patel <apatel@...tanamicro.com>
Signed-off-by: Anup Patel <anup@...infault.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/riscv/kvm/vcpu.c |    2 --
 1 file changed, 2 deletions(-)

--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -653,8 +653,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *
 				     vcpu->arch.isa);
 	kvm_riscv_vcpu_host_fp_restore(&vcpu->arch.host_context);
 
-	csr_write(CSR_HGATP, 0);
-
 	csr->vsstatus = csr_read(CSR_VSSTATUS);
 	csr->vsie = csr_read(CSR_VSIE);
 	csr->vstvec = csr_read(CSR_VSTVEC);