linux-kernel - Re: [PATCH 8/9] KVM: MMU: fix MTRR update

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Message-ID: <554B987E.2060603@redhat.com>
Date:	Thu, 07 May 2015 18:53:18 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	guangrong.xiao@...ux.intel.com
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] KVM: MMU: fix MTRR update



On 30/04/2015 12:24, guangrong.xiao@...ux.intel.com wrote:
> +static void vmx_set_msr_mtrr(struct kvm_vcpu *vcpu, u32 msr)
> +{
> +	struct mtrr_state_type *mtrr_state = &vcpu->arch.mtrr_state;
> +	unsigned char mtrr_enabled = mtrr_state->enabled;
> +	gfn_t start, end, mask;
> +	int index;
> +	bool is_fixed = true;
> +
> +	if (msr == MSR_IA32_CR_PAT || !enable_ept ||
> +	      !kvm_arch_has_noncoherent_dma(vcpu->kvm))
> +		return;
> +
> +	if (!(mtrr_enabled & 0x2) && msr != MSR_MTRRdefType)
> +		return;
> +
> +	switch (msr) {
> +	case MSR_MTRRfix64K_00000:
> +		start = 0x0;
> +		end = 0x80000;
> +		break;
> +	case MSR_MTRRfix16K_80000:
> +		start = 0x80000;
> +		end = 0xa0000;
> +		break;
> +	case MSR_MTRRfix16K_A0000:
> +		start = 0xa0000;
> +		end = 0xc0000;
> +		break;
> +	case MSR_MTRRfix4K_C0000 ... MSR_MTRRfix4K_F8000:
> +		index = msr - MSR_MTRRfix4K_C0000;
> +		start = 0xc0000 + index * (32 << 10);
> +		end = start + (32 << 10);
> +		break;
> +	case MSR_MTRRdefType:
> +		is_fixed = false;
> +		start = 0x0;
> +		end = ~0ULL;
> +		break;
> +	default:
> +		/* variable range MTRRs. */
> +		is_fixed = false;
> +		index = (msr - 0x200) / 2;
> +		start = (((u64)mtrr_state->var_ranges[index].base_hi) << 32) +
> +		       (mtrr_state->var_ranges[index].base_lo & PAGE_MASK);
> +		mask = (((u64)mtrr_state->var_ranges[index].mask_hi) << 32) +
> +		       (mtrr_state->var_ranges[index].mask_lo & PAGE_MASK);
> +		mask |= ~0ULL << cpuid_maxphyaddr(vcpu);
> +
> +		end = ((start & mask) | ~mask) + 1;
> +	}
> +
> +	if (is_fixed && !(mtrr_enabled & 0x1))
> +		return;
> +
> +	kvm_zap_gfn_range(vcpu->kvm, gpa_to_gfn(start), gpa_to_gfn(end));
> +}

I think this should all be generic logic, even if it causes some extra
zaps on AMD.  (It's AMD's bug that it doesn't honor MTRRs).

Even !enable_ept can be handled in a vendor-independent manner, as
"vcpu->arch.mmu.page_fault == tdp_page_fault".

Paolo
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