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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH V6 1/2] xen/gnttab: Store frame GFN in struct page_info on Arm
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx> Rework Arm implementation to store grant table frame GFN in struct page_info directly instead of keeping it in standalone status/shared arrays. This patch is based on the assumption that a grant table page is a xenheap page. To cover 64-bit/40-bit IPA on Arm64/Arm32 we need the space to hold 52-bit/28-bit + extra bit value respectively. In order to not grow the size of struct page_info borrow the required amount of bits from type_info's count portion which current context won't suffer (currently only 1 bit is used on Arm). Please note, to minimize code changes and avoid introducing an extra #ifdef-s to the header, we keep the same amount of bits on both subarches, although the count portion on Arm64 could be wider, so we waste some bits here. Introduce corresponding PGT_* constructs and access macro page_get(set)_xenheap_gfn. Please note, all accesses to the GFN portion of type_info field should always be protected by the P2M lock. In case when it is not feasible to satisfy that requirement (risk of deadlock, lock inversion, etc) it is important to make sure that all non-protected updates to this field are atomic. As several non-protected read accesses still exist within current code (most calls to page_get_xenheap_gfn() are not protected by the P2M lock) the subsequent patch will introduce hardening code for p2m_remove_mapping() to be called with P2M lock held in order to check any difference between what is already mapped and what is requested to be ummapped. Update existing gnttab macros to deal with GFN value according to new location. Also update the use of count portion of type_info field on Arm in share_xen_page_with_guest(). While at it, extend this simplified M2P-like approach for any xenheap pages which are proccessed in xenmem_add_to_physmap_one() except foreign ones. Update the code to set GFN portion after establishing new mapping for the xenheap page in said function and to clean GFN portion when putting a reference on that page in p2m_put_l3_page(). And for everything to work correctly introduce arch-specific initialization pattern PGT_TYPE_INFO_INITIALIZER to be applied to type_info field during initialization at alloc_heap_pages() and acquire_staticmem_pages(). The pattern's purpose on Arm is to clear the GFN portion before use, on x86 it is just a stub. This patch is intended to fix the potential issue on Arm which might happen when remapping grant-table frame. A guest (or the toolstack) will unmap the grant-table frame using XENMEM_remove_physmap. This is a generic hypercall, so on x86, we are relying on the fact the M2P entry will be cleared on removal. For architecture without the M2P, the GFN would still be present in the grant frame/status array. So on the next call to map the page, we will end up to request the P2M to remove whatever mapping was the given GFN. This could well be another mapping. Besides that, this patch simplifies arch code on Arm by removing arrays and corresponding management code and as the result gnttab_init_arch/gnttab_destroy_arch helpers and struct grant_table_arch become useless and can be dropped globally. Suggested-by: Julien Grall <jgrall@xxxxxxxxxx> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx> --- Dear @RISC-V maintainers, please note in current patch I drop arch specific helpers gnttab_init(destroy)_arch helpers as unneeded for both Arm and x86. Please let me know if you are going to reuse them in the nearest future and I will retain them. You can find the related discussions at: https://lore.kernel.org/xen-devel/93d0df14-2c8a-c2e3-8c51-54412190171c@xxxxxxx/ https://lore.kernel.org/xen-devel/1628890077-12545-1-git-send-email-olekstysh@xxxxxxxxx/ https://lore.kernel.org/xen-devel/1631652245-30746-1-git-send-email-olekstysh@xxxxxxxxx/ https://lore.kernel.org/xen-devel/1632425551-18910-1-git-send-email-olekstysh@xxxxxxxxx/ https://lore.kernel.org/xen-devel/1641424268-12968-1-git-send-email-olekstysh@xxxxxxxxx/ Changes RFC1 -> RFC2: - update patch description - add/update comments in code - clarify check in p2m_put_l3_page() - introduce arch_alloc_xenheap_page() and arch_free_xenheap_page() and drop page_arch_init() - add ASSERT to gnttab_shared_page() and gnttab_status_page() - rework changes to Arm's struct page_info: do not split type_info, allocate GFN portion by reducing count portion, create corresponding PGT_* construct, etc - update page_get_frame_gfn() and page_set_frame_gfn() - update the use of count portion on Arm - drop the leading underscore in the macro parameter names Changes RFC2 -> RFC3: - update patch description - drop PGT_count_base and MASK_INSR() in share_xen_page_with_guest() - update alloc_xenheap_page() and free_xenheap_page() for SEPARATE_XENHEAP case (Arm32) - provide an extra bit for GFN portion, to get PGT_INVALID_FRAME_GFN one bit more than the maximum number of physical address bits on Arm32 Changes RFC3 -> V4: - rebase on Jan's "gnttab: remove guest_physmap_remove_page() call from gnttab_map_frame()" - finally resolve locking question by recent Julien's suggestion, so drop the RFC tag - update comments in Arm's mm.h/p2m.c to not mention grant table - convert page_set(get)_frame_gfn to static inline func and rename them to page_set(get)_xenheap_gfn() - rename PGT_INVALID_FRAME_GFN to PGT_INVALID_XENHEAP_GFN - add ASSERT(is_xen_heap_page(...)) in page_set(get)_frame_gfn - remove BUG_ON() in arch_free_xenheap_page - remove local type_info in share_xen_page_with_guest() - remove an extra argument p2m in p2m_put_l3_page() - remove #ifdef CONFIG_GRANT_TABLE in p2m_put_l3_page() - also cover real-only pages by using p2m_is_ram instead of a check against p2m_ram_rw in p2m_put_l3_page() and use "else if" construct - call arch_free_xenheap_page() before clearing the PGC_xen_heap in free_xenheap_pages() - remove ASSERT() in gnttab_shared(status)_page and use simpler virt_to_page - remove local pg_ in gnttab_shared(status)_gfn - update patch description to reflect recent changes Changes V4 -> V5: - rebase on latest staging - update patch description - drop arch_alloc(free)_xenheap_page macro and use arch-specific initialization pattern to clear GFN portion before use - add const to struct page_info *p in page_get_xenheap_gfn - fix a breakage on Arm32 Changes V5 -> V6: - update patch description - add/update comments in code - s/PGT_TYPE_INFO_INIT_PATTERN/PGT_TYPE_INFO_INITIALIZER - define PGT_TYPE_INFO_INITIALIZER in page_alloc.c if arch doesn't define it - modify page_get_xenheap_gfn() to use ACCESS_ONCE() when reading type_info field - modify page_set_xenheap_gfn() to use cmpxchg() when changing type_info field - apply PGT_TYPE_INFO_INITIALIZER in alloc_heap_pages() and acquire_staticmem_pages() rather than altering both flavors of alloc_xenheap_pages() to make an extra assignment - simplify gnttab_shared(status)_page and gnttab_(shared)status_gfn macro - update a check in Arm's gnttab_set_frame_gfn() --- xen/arch/arm/include/asm/grant_table.h | 53 +++++++--------------------------- xen/arch/arm/include/asm/mm.h | 47 ++++++++++++++++++++++++++++-- xen/arch/arm/mm.c | 24 +++++++++++++-- xen/arch/arm/p2m.c | 7 +++-- xen/arch/x86/include/asm/grant_table.h | 5 ---- xen/common/grant_table.c | 9 ------ xen/common/page_alloc.c | 8 +++-- 7 files changed, 87 insertions(+), 66 deletions(-) diff --git a/xen/arch/arm/include/asm/grant_table.h b/xen/arch/arm/include/asm/grant_table.h index d31a4d6..16f817b 100644 --- a/xen/arch/arm/include/asm/grant_table.h +++ b/xen/arch/arm/include/asm/grant_table.h @@ -11,11 +11,6 @@ #define INITIAL_NR_GRANT_FRAMES 1U #define GNTTAB_MAX_VERSION 1 -struct grant_table_arch { - gfn_t *shared_gfn; - gfn_t *status_gfn; -}; - static inline void gnttab_clear_flags(struct domain *d, unsigned int mask, uint16_t *addr) { @@ -46,53 +41,27 @@ int replace_grant_host_mapping(unsigned long gpaddr, mfn_t mfn, #define gnttab_dom0_frames() \ min_t(unsigned int, opt_max_grant_frames, PFN_DOWN(_etext - _stext)) -#define gnttab_init_arch(gt) \ -({ \ - unsigned int ngf_ = (gt)->max_grant_frames; \ - unsigned int nsf_ = grant_to_status_frames(ngf_); \ - \ - (gt)->arch.shared_gfn = xmalloc_array(gfn_t, ngf_); \ - (gt)->arch.status_gfn = xmalloc_array(gfn_t, nsf_); \ - if ( (gt)->arch.shared_gfn && (gt)->arch.status_gfn ) \ - { \ - while ( ngf_-- ) \ - (gt)->arch.shared_gfn[ngf_] = INVALID_GFN; \ - while ( nsf_-- ) \ - (gt)->arch.status_gfn[nsf_] = INVALID_GFN; \ - } \ - else \ - gnttab_destroy_arch(gt); \ - (gt)->arch.shared_gfn ? 0 : -ENOMEM; \ -}) - -#define gnttab_destroy_arch(gt) \ - do { \ - XFREE((gt)->arch.shared_gfn); \ - XFREE((gt)->arch.status_gfn); \ - } while ( 0 ) - #define gnttab_set_frame_gfn(gt, st, idx, gfn, mfn) \ - ({ \ - int rc_ = 0; \ - gfn_t ogfn = gnttab_get_frame_gfn(gt, st, idx); \ - if ( gfn_eq(ogfn, INVALID_GFN) || gfn_eq(ogfn, gfn) || \ - (rc_ = guest_physmap_remove_page((gt)->domain, ogfn, mfn, \ - 0)) == 0 ) \ - ((st) ? (gt)->arch.status_gfn \ - : (gt)->arch.shared_gfn)[idx] = (gfn); \ - rc_; \ - }) + (gfn_eq(gfn, INVALID_GFN) \ + ? guest_physmap_remove_page((gt)->domain, \ + gnttab_get_frame_gfn(gt, st, idx), \ + mfn, 0) \ + : 0) #define gnttab_get_frame_gfn(gt, st, idx) ({ \ (st) ? gnttab_status_gfn(NULL, gt, idx) \ : gnttab_shared_gfn(NULL, gt, idx); \ }) +#define gnttab_shared_page(t, i) virt_to_page((t)->shared_raw[i]) + +#define gnttab_status_page(t, i) virt_to_page((t)->status[i]) + #define gnttab_shared_gfn(d, t, i) \ - (((i) >= nr_grant_frames(t)) ? INVALID_GFN : (t)->arch.shared_gfn[i]) + page_get_xenheap_gfn(gnttab_shared_page(t, i)) #define gnttab_status_gfn(d, t, i) \ - (((i) >= nr_status_frames(t)) ? INVALID_GFN : (t)->arch.status_gfn[i]) + page_get_xenheap_gfn(gnttab_status_page(t, i)) #define gnttab_need_iommu_mapping(d) \ (is_domain_direct_mapped(d) && is_iommu_enabled(d)) diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h index 424aaf2..412200a 100644 --- a/xen/arch/arm/include/asm/mm.h +++ b/xen/arch/arm/include/asm/mm.h @@ -98,9 +98,22 @@ struct page_info #define PGT_writable_page PG_mask(1, 1) /* has writable mappings? */ #define PGT_type_mask PG_mask(1, 1) /* Bits 31 or 63. */ - /* Count of uses of this frame as its current type. */ -#define PGT_count_width PG_shift(2) -#define PGT_count_mask ((1UL<<PGT_count_width)-1) + /* 2-bit count of uses of this frame as its current type. */ +#define PGT_count_mask PG_mask(3, 3) + +/* + * Stored in bits [28:0] (arm32) or [60:0] (arm64) GFN if page is xenheap page. + */ +#define PGT_gfn_width PG_shift(3) +#define PGT_gfn_mask ((1UL<<PGT_gfn_width)-1) + +#define PGT_INVALID_XENHEAP_GFN _gfn(PGT_gfn_mask) + +/* + * An arch-specific initialization pattern is needed for the type_info field + * as it's GFN portion can contain the valid GFN if page is xenheap page. + */ +#define PGT_TYPE_INFO_INITIALIZER gfn_x(PGT_INVALID_XENHEAP_GFN) /* Cleared when the owning guest 'frees' this page. */ #define _PGC_allocated PG_shift(1) @@ -358,6 +371,34 @@ void clear_and_clean_page(struct page_info *page); unsigned int arch_get_dma_bitsize(void); +/* + * All accesses to the GFN portion of type_info field should always be + * protected by the P2M lock. In case when it is not feasible to satisfy + * that requirement (risk of deadlock, lock inversion, etc) it is important + * to make sure that all non-protected updates to this field are atomic. + */ +static inline gfn_t page_get_xenheap_gfn(const struct page_info *p) +{ + gfn_t gfn_ = _gfn(ACCESS_ONCE(p->u.inuse.type_info) & PGT_gfn_mask); + + ASSERT(is_xen_heap_page(p)); + + return gfn_eq(gfn_, PGT_INVALID_XENHEAP_GFN) ? INVALID_GFN : gfn_; +} + +static inline void page_set_xenheap_gfn(struct page_info *p, gfn_t gfn) +{ + gfn_t gfn_ = gfn_eq(gfn, INVALID_GFN) ? PGT_INVALID_XENHEAP_GFN : gfn; + unsigned long x, nx, y = p->u.inuse.type_info; + + ASSERT(is_xen_heap_page(p)); + + do { + x = y; + nx = (x & ~PGT_gfn_mask) | gfn_x(gfn_); + } while ( (y = cmpxchg(&p->u.inuse.type_info, x, nx)) != x ); +} + #endif /* __ARCH_ARM_MM__ */ /* * Local variables: diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 7b1f2f4..c94bdaf 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -1400,8 +1400,10 @@ void share_xen_page_with_guest(struct page_info *page, struct domain *d, spin_lock(&d->page_alloc_lock); /* The incremented type count pins as writable or read-only. */ - page->u.inuse.type_info = - (flags == SHARE_ro ? PGT_none : PGT_writable_page) | 1; + page->u.inuse.type_info &= ~(PGT_type_mask | PGT_count_mask); + page->u.inuse.type_info |= (flags == SHARE_ro ? PGT_none + : PGT_writable_page) | + MASK_INSR(1, PGT_count_mask); page_set_owner(page, d); smp_wmb(); /* install valid domain ptr before updating refcnt. */ @@ -1505,7 +1507,23 @@ int xenmem_add_to_physmap_one( } /* Map at new location. */ - rc = guest_physmap_add_entry(d, gfn, mfn, 0, t); + if ( !p2m_is_ram(t) || !is_xen_heap_mfn(mfn) ) + rc = guest_physmap_add_entry(d, gfn, mfn, 0, t); + else + { + struct p2m_domain *p2m = p2m_get_hostp2m(d); + + p2m_write_lock(p2m); + if ( gfn_eq(page_get_xenheap_gfn(mfn_to_page(mfn)), INVALID_GFN) ) + { + rc = p2m_set_entry(p2m, gfn, 1, mfn, t, p2m->default_access); + if ( !rc ) + page_set_xenheap_gfn(mfn_to_page(mfn), gfn); + } + else + rc = -EBUSY; + p2m_write_unlock(p2m); + } /* * For XENMAPSPACE_gmfn_foreign if we failed to add the mapping, we need diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c index d00c2e4..f87b48e 100644 --- a/xen/arch/arm/p2m.c +++ b/xen/arch/arm/p2m.c @@ -716,6 +716,8 @@ static int p2m_mem_access_radix_set(struct p2m_domain *p2m, gfn_t gfn, */ static void p2m_put_l3_page(const lpae_t pte) { + mfn_t mfn = lpae_get_mfn(pte); + ASSERT(p2m_is_valid(pte)); /* @@ -727,11 +729,12 @@ static void p2m_put_l3_page(const lpae_t pte) */ if ( p2m_is_foreign(pte.p2m.type) ) { - mfn_t mfn = lpae_get_mfn(pte); - ASSERT(mfn_valid(mfn)); put_page(mfn_to_page(mfn)); } + /* Detect the xenheap page and mark the stored GFN as invalid. */ + else if ( p2m_is_ram(pte.p2m.type) && is_xen_heap_mfn(mfn) ) + page_set_xenheap_gfn(mfn_to_page(mfn), INVALID_GFN); } /* Free lpae sub-tree behind an entry */ diff --git a/xen/arch/x86/include/asm/grant_table.h b/xen/arch/x86/include/asm/grant_table.h index a8a2143..5c23cec 100644 --- a/xen/arch/x86/include/asm/grant_table.h +++ b/xen/arch/x86/include/asm/grant_table.h @@ -14,9 +14,6 @@ #define INITIAL_NR_GRANT_FRAMES 1U -struct grant_table_arch { -}; - static inline int create_grant_host_mapping(uint64_t addr, mfn_t frame, unsigned int flags, unsigned int cache_flags) @@ -35,8 +32,6 @@ static inline int replace_grant_host_mapping(uint64_t addr, mfn_t frame, return replace_grant_pv_mapping(addr, frame, new_addr, flags); } -#define gnttab_init_arch(gt) 0 -#define gnttab_destroy_arch(gt) do {} while ( 0 ) #define gnttab_set_frame_gfn(gt, st, idx, gfn, mfn) \ (gfn_eq(gfn, INVALID_GFN) \ ? guest_physmap_remove_page((gt)->domain, \ diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c index febbe12..4115da0 100644 --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -99,8 +99,6 @@ struct grant_table { /* Domain to which this struct grant_table belongs. */ struct domain *domain; - - struct grant_table_arch arch; }; unsigned int __read_mostly opt_max_grant_frames = 64; @@ -2018,14 +2016,9 @@ int grant_table_init(struct domain *d, int max_grant_frames, grant_write_lock(gt); - ret = gnttab_init_arch(gt); - if ( ret ) - goto unlock; - /* gnttab_grow_table() allocates a min number of frames, so 0 is okay. */ ret = gnttab_grow_table(d, 0); - unlock: grant_write_unlock(gt); out: @@ -3940,8 +3933,6 @@ grant_table_destroy( if ( t == NULL ) return; - gnttab_destroy_arch(t); - for ( i = 0; i < nr_grant_frames(t); i++ ) free_xenheap_page(t->shared_raw[i]); xfree(t->shared_raw); diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index 3190291..dbacee2 100644 --- a/xen/common/page_alloc.c +++ b/xen/common/page_alloc.c @@ -155,6 +155,10 @@ #define PGC_reserved 0 #endif +#ifndef PGT_TYPE_INFO_INITIALIZER +#define PGT_TYPE_INFO_INITIALIZER 0 +#endif + /* * Comma-separated list of hexadecimal page numbers containing bad bytes. * e.g. 'badpage=0x3f45,0x8a321'. @@ -1024,7 +1028,7 @@ static struct page_info *alloc_heap_pages( &tlbflush_timestamp); /* Initialise fields which have other uses for free pages. */ - pg[i].u.inuse.type_info = 0; + pg[i].u.inuse.type_info = PGT_TYPE_INFO_INITIALIZER; page_set_owner(&pg[i], NULL); } @@ -2702,7 +2706,7 @@ static struct page_info * __init acquire_staticmem_pages(mfn_t smfn, */ pg[i].count_info = PGC_reserved | PGC_state_inuse; /* Initialise fields which have other uses for free pages. */ - pg[i].u.inuse.type_info = 0; + pg[i].u.inuse.type_info = PGT_TYPE_INFO_INITIALIZER; page_set_owner(&pg[i], NULL); } -- 2.7.4
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