kvm: x86/mmu: Introduce tdp_iter

kvm-y			+= x86.o emulate.o i8259.o irq.o lapic.o \

			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \

			   hyperv.o debugfs.o mmu/mmu.o mmu/page_track.o \

			   mmu/spte.o

			   mmu/spte.o mmu/tdp_iter.o

kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \

			   vmx/evmcs.o vmx/nested.o vmx/posted_intr.o

// SPDX-License-Identifier: GPL-2.0

#include "mmu_internal.h"

#include "tdp_iter.h"

#include "spte.h"

/*

 * Recalculates the pointer to the SPTE for the current GFN and level and

 * reread the SPTE.

 */

static void tdp_iter_refresh_sptep(struct tdp_iter *iter)

{

	iter->sptep = iter->pt_path[iter->level - 1] +

		SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level);

	iter->old_spte = READ_ONCE(*iter->sptep);

}

static gfn_t round_gfn_for_level(gfn_t gfn, int level)

{

	return gfn & -KVM_PAGES_PER_HPAGE(level);

}

/*

 * Sets a TDP iterator to walk a pre-order traversal of the paging structure

 * rooted at root_pt, starting with the walk to translate goal_gfn.

 */

void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,

		    int min_level, gfn_t goal_gfn)

{

	WARN_ON(root_level < 1);

	WARN_ON(root_level > PT64_ROOT_MAX_LEVEL);

	iter->goal_gfn = goal_gfn;

	iter->root_level = root_level;

	iter->min_level = min_level;

	iter->level = root_level;

	iter->pt_path[iter->level - 1] = root_pt;

	iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level);

	tdp_iter_refresh_sptep(iter);

	iter->valid = true;

}

/*

 * Given an SPTE and its level, returns a pointer containing the host virtual

 * address of the child page table referenced by the SPTE. Returns null if

 * there is no such entry.

 */

u64 *spte_to_child_pt(u64 spte, int level)

{

	/*

	 * There's no child entry if this entry isn't present or is a

	 * last-level entry.

	 */

	if (!is_shadow_present_pte(spte) || is_last_spte(spte, level))

		return NULL;

	return __va(spte_to_pfn(spte) << PAGE_SHIFT);

}

/*

 * Steps down one level in the paging structure towards the goal GFN. Returns

 * true if the iterator was able to step down a level, false otherwise.

 */

static bool try_step_down(struct tdp_iter *iter)

{

	u64 *child_pt;

	if (iter->level == iter->min_level)

		return false;

	/*

	 * Reread the SPTE before stepping down to avoid traversing into page

	 * tables that are no longer linked from this entry.

	 */

	iter->old_spte = READ_ONCE(*iter->sptep);

	child_pt = spte_to_child_pt(iter->old_spte, iter->level);

	if (!child_pt)

		return false;

	iter->level--;

	iter->pt_path[iter->level - 1] = child_pt;

	iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level);

	tdp_iter_refresh_sptep(iter);

	return true;

}

/*

 * Steps to the next entry in the current page table, at the current page table

 * level. The next entry could point to a page backing guest memory or another

 * page table, or it could be non-present. Returns true if the iterator was

 * able to step to the next entry in the page table, false if the iterator was

 * already at the end of the current page table.

 */

static bool try_step_side(struct tdp_iter *iter)

{

	/*

	 * Check if the iterator is already at the end of the current page

	 * table.

	 */

	if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==

            (PT64_ENT_PER_PAGE - 1))

		return false;

	iter->gfn += KVM_PAGES_PER_HPAGE(iter->level);

	iter->goal_gfn = iter->gfn;

	iter->sptep++;

	iter->old_spte = READ_ONCE(*iter->sptep);

	return true;

}

/*

 * Tries to traverse back up a level in the paging structure so that the walk

 * can continue from the next entry in the parent page table. Returns true on a

 * successful step up, false if already in the root page.

 */

static bool try_step_up(struct tdp_iter *iter)

{

	if (iter->level == iter->root_level)

		return false;

	iter->level++;

	iter->gfn = round_gfn_for_level(iter->gfn, iter->level);

	tdp_iter_refresh_sptep(iter);

	return true;

}

/*

 * Step to the next SPTE in a pre-order traversal of the paging structure.

 * To get to the next SPTE, the iterator either steps down towards the goal

 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a

 * highter GFN.

 *

 * The basic algorithm is as follows:

 * 1. If the current SPTE is a non-last-level SPTE, step down into the page

 *    table it points to.

 * 2. If the iterator cannot step down, it will try to step to the next SPTE

 *    in the current page of the paging structure.

 * 3. If the iterator cannot step to the next entry in the current page, it will

 *    try to step up to the parent paging structure page. In this case, that

 *    SPTE will have already been visited, and so the iterator must also step

 *    to the side again.

 */

void tdp_iter_next(struct tdp_iter *iter)

{

	if (try_step_down(iter))

		return;

	do {

		if (try_step_side(iter))

			return;

	} while (try_step_up(iter));

	iter->valid = false;

}

/*

 * Restart the walk over the paging structure from the root, starting from the

 * highest gfn the iterator had previously reached. Assumes that the entire

 * paging structure, except the root page, may have been completely torn down

 * and rebuilt.

 */

void tdp_iter_refresh_walk(struct tdp_iter *iter)

{

	gfn_t goal_gfn = iter->goal_gfn;

	if (iter->gfn > goal_gfn)

		goal_gfn = iter->gfn;

	tdp_iter_start(iter, iter->pt_path[iter->root_level - 1],

		       iter->root_level, iter->min_level, goal_gfn);

}

// SPDX-License-Identifier: GPL-2.0

#ifndef __KVM_X86_MMU_TDP_ITER_H

#define __KVM_X86_MMU_TDP_ITER_H

#include <linux/kvm_host.h>

#include "mmu.h"

/*

 * A TDP iterator performs a pre-order walk over a TDP paging structure.

 */

struct tdp_iter {

	/*

	 * The iterator will traverse the paging structure towards the mapping

	 * for this GFN.

	 */

	gfn_t goal_gfn;

	/* Pointers to the page tables traversed to reach the current SPTE */

	u64 *pt_path[PT64_ROOT_MAX_LEVEL];

	/* A pointer to the current SPTE */

	u64 *sptep;

	/* The lowest GFN mapped by the current SPTE */

	gfn_t gfn;

	/* The level of the root page given to the iterator */

	int root_level;

	/* The lowest level the iterator should traverse to */

	int min_level;

	/* The iterator's current level within the paging structure */

	int level;

	/* A snapshot of the value at sptep */

	u64 old_spte;

	/*

	 * Whether the iterator has a valid state. This will be false if the

	 * iterator walks off the end of the paging structure.

	 */

	bool valid;

};

/*

 * Iterates over every SPTE mapping the GFN range [start, end) in a

 * preorder traversal.

 */

#define for_each_tdp_pte(iter, root, root_level, start, end) \

	for (tdp_iter_start(&iter, root, root_level, PG_LEVEL_4K, start); \

	     iter.valid && iter.gfn < end;		     \

	     tdp_iter_next(&iter))

u64 *spte_to_child_pt(u64 pte, int level);

void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,

		    int min_level, gfn_t goal_gfn);

void tdp_iter_next(struct tdp_iter *iter);

void tdp_iter_refresh_walk(struct tdp_iter *iter);

#endif /* __KVM_X86_MMU_TDP_ITER_H */