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keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <20260603130603.776452-13-frediano.ziglio@cloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-purgate-ID: tlsNG-ef75cf/1780493996-20F66C48-68D30F43/0/0 X-purgate-type: clean X-purgate-size: 7127 On 03.06.2026 15:05, Frediano Ziglio wrote: > --- a/xen/common/memory.c > +++ b/xen/common/memory.c > @@ -1545,6 +1545,132 @@ static int acquire_resource( > return rc; > } > > +/* > + * The "noinline" qualifier avoid the compiler to create a large function > + * consuming quite a lot of stack. > + */ > +static int noinline mem_foreigncopy( > + XEN_GUEST_HANDLE_PARAM(xen_foreigncopy_t) arg) > +{ > + struct domain *d, *const currd = current->domain; > + xen_foreigncopy_t copy; > + int rc, direction; > + > + if ( !arch_acquire_resource_check(currd) ) > + return -EACCES; How is the new sub-op related to acquire-resource? And aren't you instead lacking an XSM check? > + if ( copy_from_guest(©, arg, 1) ) > + return -EFAULT; > + > + if ( copy.flags & ~1u ) If a suffix is needed here in the first place, please use an upper-case one. Misra only demands L suffixes to be upper-case, but iirc we decided that then we want all suffixes that way. > + return -EINVAL; > + > + direction = copy.flags & XENMEM_foreigncopy_direction; > + > + if ( copy.nr_frames == 0 ) > + return 0; > + > + rc = rcu_lock_remote_domain_by_id(copy.domid, &d); Why not rcu_lock_domain_by_any_id()? IOW why would a self-copy need prohibiting? > + if ( rc ) > + return rc; > + > + /* > + * Check we are allowed to map and access these foreign pages. > + */ > + rc = xsm_map_gmfn_foreign(XSM_TARGET, currd, d); > + if ( rc ) > + goto out; > + > + do { > + /* > + * Arbitrary size. Not too much stack space, and a reasonable stride > + * for continuation checks. > + */ > + xen_pfn_t gfn_list[32]; > + unsigned int todo = MIN(ARRAY_SIZE(gfn_list), copy.nr_frames); > + > + rc = -EFAULT; > + if ( copy_from_guest(gfn_list, copy.frame_list, todo) ) > + goto out; > + > + for ( unsigned i = 0; i < todo; i++ ) > + { > + struct page_info *foreign_page; > + void *foreign; > + p2m_type_t p2mt; > + > + foreign_page = get_page_from_gfn(d, gfn_list[i], &p2mt, P2M_ALLOC); > + > + if ( unlikely(p2mt != p2m_ram_rw > +#ifdef CONFIG_X86 > + && p2mt != p2m_ram_logdirty > +#endif > + ) && foreign_page ) This is ugly formatting wise, and the use of unlikely() isn't very likely to have the effect you intend: As long as the compiler can't translate the && expression to something involving only a single conditional branch, which of the branches is it that is unlikely to be taken? > + { > + put_page(foreign_page); > + foreign_page = NULL; > + } > + if ( unlikely(!foreign_page) ) > + { > + gdprintk(XENLOG_WARNING, > + "Error accessing foreign mfn %" PRI_mfn "\n", > + gfn_list[i]); As per get_page_from_gfn() and gfn_list[] it's a GFN, not an MFN. > + rc = -EINVAL; > + copy.nr_frames -= i; > + guest_handle_add_offset(copy.frame_list, i); > + goto out; > + } > + > + /* A page is dirtied when it's being copied to. */ > + if ( direction == XENMEM_foreigncopy_to ) > + paging_mark_dirty(d, page_to_mfn(foreign_page)); > + > + foreign = map_domain_page(page_to_mfn(foreign_page)); > + if ( direction == XENMEM_foreigncopy_from ) > + rc = copy_to_guest(copy.buffer, foreign, PAGE_SIZE); > + else > + rc = copy_from_guest(foreign, copy.buffer, PAGE_SIZE); > + unmap_domain_page(foreign); > + put_page(foreign_page); > + > + if ( unlikely(rc) ) > + { > + gdprintk(XENLOG_WARNING, > + "Error copying to mfn %" PRI_mfn "\n", gfn_list[i]); "to" isn't always correct here, and the problem wasn't with the GFN (not MFN) anyway, but with the buffer. > + copy.nr_frames -= i; > + guest_handle_add_offset(copy.frame_list, i); > + goto out; > + } > + > + guest_handle_add_offset(copy.buffer, PAGE_SIZE); > + } > + > + copy.nr_frames -= todo; > + guest_handle_add_offset(copy.frame_list, todo); > + > + if ( copy.nr_frames && hypercall_preempt_check() ) > + { > + rc = hypercall_create_continuation( > + __HYPERVISOR_memory_op, "lh", XENMEM_foreigncopy, arg); > + goto out; > + } > + } while ( copy.nr_frames ); > + > + rc = 0; > + > + out: > + rcu_unlock_domain(d); > + > + /* Update in all cases, it allows the caller to know how many > + * frames were successfully copied and the continuation to > + * continue correctly. > + */ > + if ( copy_to_guest(arg, ©, 1) ) Since you already used copy_from_guest() one the way in, __copy_to_guest() will do here. > + rc = -EFAULT; > + > + return rc; > +} Before looking at the implementation in yet more detail: This is quite a bit of new code. Did you at least consider extending MMUEXT_COPY_PAGE along the lines of what c6b8bdfe3b47 ("x86: extend mmu_update hypercall to allow update of foreign pagetables") did, allowing two domains to be specified in the foreigndom argument? > @@ -2012,6 +2138,13 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg) > start_extent); > break; > > + case XENMEM_foreigncopy: > + if ( unlikely(start_extent) ) > + return -EINVAL; Why make this different from other continuable sub-ops? > --- a/xen/include/public/memory.h > +++ b/xen/include/public/memory.h > @@ -740,7 +740,45 @@ struct xen_vnuma_topology_info { > typedef struct xen_vnuma_topology_info xen_vnuma_topology_info_t; > DEFINE_XEN_GUEST_HANDLE(xen_vnuma_topology_info_t); > > -/* Next available subop number is 29 */ > +/* > + * Copy memory from/to a given domain. > + */ > +#define XENMEM_foreigncopy 29 > +struct xen_foreigncopy { > + /* IN - The domain whose resource is to be copied. */ > + domid_t domid; > + > + /* IN - Flags. */ > +#define XENMEM_foreigncopy_from 0 > +#define XENMEM_foreigncopy_to 1 > +#define XENMEM_foreigncopy_direction 1 > + uint16_t flags; > + > + /* > + * IN > + * > + * As an IN parameter number of frames of the domain to be copied. > + */ > + uint32_t nr_frames; > + > + /* > + * IN > + * > + * Frames to be copied. > + */ > + XEN_GUEST_HANDLE(xen_pfn_t) frame_list; > + > + /* > + * IN/OUT > + * > + * Userspace buffer to read/write from. > + */ > + XEN_GUEST_HANDLE(uint8) buffer; > +}; Seeing the two handles - what about compat_memory_op()? Jan