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Subject: Re: [PATCH v4 2/4] migration: API to clear bits of guest free pages from the dirty bitmap
On 03/15/2018 02:11 AM, Dr. David Alan Gilbert wrote:
* Wei Wang (wei.w.wang@intel.com) wrote:This patch adds an API to clear bits corresponding to guest free pages from the dirty bitmap. Spilt the free page block if it crosses the QEMU RAMBlock boundary. Signed-off-by: Wei Wang <wei.w.wang@intel.com> CC: Dr. David Alan Gilbert <dgilbert@redhat.com> CC: Juan Quintela <quintela@redhat.com> CC: Michael S. Tsirkin <mst@redhat.com> --- include/migration/misc.h | 2 ++ migration/ram.c | 21 +++++++++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/include/migration/misc.h b/include/migration/misc.h index 77fd4f5..fae1acf 100644 --- a/include/migration/misc.h +++ b/include/migration/misc.h @@ -14,11 +14,13 @@ #ifndef MIGRATION_MISC_H #define MIGRATION_MISC_H+#include "exec/cpu-common.h"#include "qemu/notify.h"/* migration/ram.c */ void ram_mig_init(void);+void qemu_guest_free_page_hint(void *addr, size_t len);/* migration/block.c */ diff --git a/migration/ram.c b/migration/ram.cindex 5e33e5c..e172798 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -2189,6 +2189,27 @@ static int ram_init_all(RAMState **rsp) return 0; }This could do with some comments
OK, I'll add some.
+void qemu_guest_free_page_hint(void *addr, size_t len) +{ + RAMBlock *block; + ram_addr_t offset; + size_t used_len, start, npages;From your use I think the addr and len are coming raw from the guest; so we need to take some care.
Actually the "addr" here has been the host address that corresponds to the guest free page. It's from elem->in_sg[0].iov_base.
+ if (unlikely(offset + len > block->used_length)) {I think to make that overflow safe, that should be: if (len > (block->used_length - offset)) { But we'll need another test before it, because qemu_ram_block_from_host seems to check max_length not used_length, so we need to check for offset > block->used_length first
OK, how about adding an assert above, like this: block = qemu_ram_block_from_host(addr, false, &offset); assert (offset < block->used_length ); if (!block) ...The address corresponds to a guest free page, which means it should be within used_length. If not, something weird happens, I think we'd better to assert it in that case.
Best, Wei
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