Commit 905f5ce0 authored by David Hildenbrand's avatar David Hildenbrand Committed by Claudio Imbrenda
Browse files

KVM: s390: vsie: stop messing with page refcount 



Let's stop messing with the page refcount, and use a flag that is set /
cleared atomically to remember whether a vsie page is currently in use.

Note that we could use a page flag, or a lower bit of the scb_gpa. Let's
keep it simple for now, we have sufficient space.

While at it, stop passing "struct kvm *" to put_vsie_page(), it's
unused.

Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: default avatarChristoph Schlameuss <schlameuss@linux.ibm.com>
Tested-by: default avatarChristoph Schlameuss <schlameuss@linux.ibm.com>
Message-ID: <20250107154344.1003072-4-david@redhat.com>
Signed-off-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
parent c5f64c98

arch/s390/kvm/vsie.c

+30 −16
Original line number Diff line number Diff line
@@ -23,6 +23,10 @@ 
#include "kvm-s390.h"

#include "gaccess.h"



enum vsie_page_flags {

	VSIE_PAGE_IN_USE = 0,

};



struct vsie_page {

	struct kvm_s390_sie_block scb_s;	/* 0x0000 */

	/*
@@ -52,7 +56,12 @@ struct vsie_page { 
	 * radix tree.

	 */

	gpa_t scb_gpa;				/* 0x0258 */

	__u8 reserved[0x0700 - 0x0260];		/* 0x0260 */

	/*

	 * Flags: must be set/cleared atomically after the vsie page can be

	 * looked up by other CPUs.

	 */

	unsigned long flags;			/* 0x0260 */

	__u8 reserved[0x0700 - 0x0268];		/* 0x0268 */

	struct kvm_s390_crypto_cb crycb;	/* 0x0700 */

	__u8 fac[S390_ARCH_FAC_LIST_SIZE_BYTE];	/* 0x0800 */

};
@@ -1351,6 +1360,20 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) 
	return rc;

}



/* Try getting a given vsie page, returning "true" on success. */

static inline bool try_get_vsie_page(struct vsie_page *vsie_page)

{

	if (test_bit(VSIE_PAGE_IN_USE, &vsie_page->flags))

		return false;

	return !test_and_set_bit(VSIE_PAGE_IN_USE, &vsie_page->flags);

}



/* Put a vsie page acquired through get_vsie_page / try_get_vsie_page. */

static void put_vsie_page(struct vsie_page *vsie_page)

{

	clear_bit(VSIE_PAGE_IN_USE, &vsie_page->flags);

}



/*

 * Get or create a vsie page for a scb address.

 *
@@ -1369,15 +1392,15 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) 
	rcu_read_unlock();

	if (page) {

		vsie_page = page_to_virt(page);

		if (page_ref_inc_return(page) == 2) {

		if (try_get_vsie_page(vsie_page)) {

			if (vsie_page->scb_gpa == addr)

				return vsie_page;

			/*

			 * We raced with someone reusing + putting this vsie

			 * page before we grabbed it.

			 */

			put_vsie_page(vsie_page);

		}

		page_ref_dec(page);

	}



	/*
@@ -1394,7 +1417,7 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) 
			return ERR_PTR(-ENOMEM);

		}

		vsie_page = page_to_virt(page);

		page_ref_inc(page);

		__set_bit(VSIE_PAGE_IN_USE, &vsie_page->flags);

		kvm->arch.vsie.pages[kvm->arch.vsie.page_count] = page;

		kvm->arch.vsie.page_count++;

	} else {
@@ -1402,9 +1425,8 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) 
		while (true) {

			page = kvm->arch.vsie.pages[kvm->arch.vsie.next];

			vsie_page = page_to_virt(page);

			if (page_ref_inc_return(page) == 2)

			if (try_get_vsie_page(vsie_page))

				break;

			page_ref_dec(page);

			kvm->arch.vsie.next++;

			kvm->arch.vsie.next %= nr_vcpus;

		}
@@ -1417,7 +1439,7 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) 


	/* Double use of the same address or allocation failure. */

	if (radix_tree_insert(&kvm->arch.vsie.addr_to_page, addr >> 9, page)) {

		page_ref_dec(page);

		put_vsie_page(vsie_page);

		mutex_unlock(&kvm->arch.vsie.mutex);

		return NULL;

	}
@@ -1431,14 +1453,6 @@ static struct vsie_page *get_vsie_page(struct kvm *kvm, unsigned long addr) 
	return vsie_page;

}



/* put a vsie page acquired via get_vsie_page */

static void put_vsie_page(struct kvm *kvm, struct vsie_page *vsie_page)

{

	struct page *page = pfn_to_page(__pa(vsie_page) >> PAGE_SHIFT);



	page_ref_dec(page);

}



int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu)

{

	struct vsie_page *vsie_page;
@@ -1489,7 +1503,7 @@ int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu) 
out_unpin_scb:

	unpin_scb(vcpu, vsie_page, scb_addr);

out_put:

	put_vsie_page(vcpu->kvm, vsie_page);

	put_vsie_page(vsie_page);



	return rc < 0 ? rc : 0;

}