linux-kernel - Re: [RESEND PATCH v10 03/10] mmu: spp: Add SPP Table setup functions

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Message-ID: <20200110172611.GC21485@linux.intel.com>
Date:   Fri, 10 Jan 2020 09:26:11 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, jmattson@...gle.com,
        yu.c.zhang@...ux.intel.com, alazar@...defender.com,
        edwin.zhai@...el.com
Subject: Re: [RESEND PATCH v10 03/10] mmu: spp: Add SPP Table setup functions

On Thu, Jan 02, 2020 at 02:13:12PM +0800, Yang Weijiang wrote:
> SPPT is a 4-level paging structure similar to EPT, when SPP is

How does SPP interact with 5-level EPT?

> armed for target physical page, bit 61 of the corresponding
> EPT entry is flaged, then SPPT is traversed with the gfn,
> the leaf entry of SPPT contains the access bitmap of subpages
> inside the target 4KB physical page, one bit per 128-byte subpage.
> 
> Co-developed-by: He Chen <he.chen@...ux.intel.com>
> Signed-off-by: He Chen <he.chen@...ux.intel.com>
> Co-developed-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Zhang Yi <yi.z.zhang@...ux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---

...

> +static u64 format_spp_spte(u32 spp_wp_bitmap)
> +{
> +	u64 new_spte = 0;
> +	int i = 0;
> +
> +	/*
> +	 * One 4K page contains 32 sub-pages, in SPP table L4E, old bits

Is this

	One 4k page constains 32 sub-pages in SPP table L4E.  Old bits are...

or
	One 4k page contains 32 sub-pages.  In SPP table L4E, old bits are...

or
	???

> +	 * are reserved, so we need to transfer u32 subpage write

Wrap comments at 80 columns to save lines.

> +	 * protect bitmap to u64 SPP L4E format.

What is a "page" in "one 4k page"?  What old bits?  Why not just track a
64-bit value?  I understand *what* the code below does, but I have no clue
why or whether it's correct.

> +	 */
> +	while (i < 32) {
> +		if (spp_wp_bitmap & (1ULL << i))
> +			new_spte |= 1ULL << (i * 2);
> +		i++;
> +	}

	for (i = 0; i < 32; i++)
		new_spte |= (spp_wp_bitmap & BIT_ULL(i)) << i;

At the very least, use a for loop.

> +
> +	return new_spte;
> +}
> +
> +static void spp_spte_set(u64 *sptep, u64 new_spte)
> +{
> +	__set_spte(sptep, new_spte);
> +}
> +
> +bool is_spp_spte(struct kvm_mmu_page *sp)
> +{
> +	return sp->role.spp;
> +}
> +
> +#define SPPT_ENTRY_PHA_MASK (0xFFFFFFFFFF << 12)
> +
> +int kvm_spp_setup_structure(struct kvm_vcpu *vcpu,
> +			    u32 access_map, gfn_t gfn)
> +{
> +	struct kvm_shadow_walk_iterator iter;
> +	struct kvm_mmu_page *sp;
> +	gfn_t pseudo_gfn;
> +	u64 old_spte, spp_spte;
> +	int ret = -EFAULT;
> +
> +	/* direct_map spp start */
> +	if (!VALID_PAGE(vcpu->kvm->arch.sppt_root))
> +		return -EFAULT;
> +
> +	for_each_shadow_spp_entry(vcpu, (u64)gfn << PAGE_SHIFT, iter) {
> +		if (iter.level == PT_PAGE_TABLE_LEVEL) {
> +			spp_spte = format_spp_spte(access_map);
> +			old_spte = mmu_spte_get_lockless(iter.sptep);
> +			if (old_spte != spp_spte)
> +				spp_spte_set(iter.sptep, spp_spte);
> +			ret = 0;
> +			break;
> +		}
> +
> +		if (!is_shadow_present_pte(*iter.sptep)) {
> +			u64 base_addr = iter.addr;
> +
> +			base_addr &= PT64_LVL_ADDR_MASK(iter.level);
> +			pseudo_gfn = base_addr >> PAGE_SHIFT;
> +			spp_spte = *iter.sptep;
> +			sp = kvm_spp_get_page(vcpu, pseudo_gfn,
> +					      iter.level - 1);
> +			link_spp_shadow_page(vcpu, iter.sptep, sp);
> +		} else if (iter.level == PT_DIRECTORY_LEVEL  &&
> +			   !(spp_spte & PT_PRESENT_MASK) &&
> +			   (spp_spte & SPPT_ENTRY_PHA_MASK)) {
> +			spp_spte = *iter.sptep;
> +			spp_spte |= PT_PRESENT_MASK;
> +			spp_spte_set(iter.sptep, spp_spte);
> +		}
> +	}
> +
> +	kvm_flush_remote_tlbs(vcpu->kvm);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(kvm_spp_setup_structure);
> +
> +inline u64 construct_spptp(unsigned long root_hpa)
> +{
> +	return root_hpa & PAGE_MASK;
> +}
> +EXPORT_SYMBOL_GPL(construct_spptp);
> +
> diff --git a/arch/x86/kvm/mmu/spp.h b/arch/x86/kvm/mmu/spp.h
> new file mode 100644
> index 000000000000..8ef94b7a2057
> --- /dev/null
> +++ b/arch/x86/kvm/mmu/spp.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __KVM_X86_VMX_SPP_H
> +#define __KVM_X86_VMX_SPP_H
> +
> +bool is_spp_spte(struct kvm_mmu_page *sp);
> +u64 construct_spptp(unsigned long root_hpa);
> +int kvm_spp_setup_structure(struct kvm_vcpu *vcpu,
> +			    u32 access_map, gfn_t gfn);
> +
> +#endif /* __KVM_X86_VMX_SPP_H */
> -- 
> 2.17.2
>