git: 1d528f95e8ce - main - xen/blkback: remove bounce buffering mode
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Date: Tue, 07 Jun 2022 10:30:03 UTC
The branch main has been updated by royger:
URL: https://cgit.FreeBSD.org/src/commit/?id=1d528f95e8ce4f2b11f63a3e3aa4bca14df1eb51
commit 1d528f95e8ce4f2b11f63a3e3aa4bca14df1eb51
Author: Roger Pau Monné <royger@FreeBSD.org>
AuthorDate: 2022-04-12 14:17:09 +0000
Commit: Roger Pau Monné <royger@FreeBSD.org>
CommitDate: 2022-06-07 10:29:53 +0000
xen/blkback: remove bounce buffering mode
Remove bounce buffering code for blkback and only attach if Xen
creates IOMMU entries for grant mapped pages.
Such bounce buffering consumed a non trivial amount of memory and CPU
resources to do the memory copy, when it's been a long time since Xen
has been creating IOMMU entries for grant maps.
Refuse to attach blkback if Xen doesn't advertise that IOMMU entries
are created for grant maps.
Sponsored by: Citrix Systems R&D
---
sys/dev/xen/blkback/blkback.c | 200 +++++-------------------------------------
1 file changed, 22 insertions(+), 178 deletions(-)
diff --git a/sys/dev/xen/blkback/blkback.c b/sys/dev/xen/blkback/blkback.c
index fa0bb3ff85ed..b15dbb1e9155 100644
--- a/sys/dev/xen/blkback/blkback.c
+++ b/sys/dev/xen/blkback/blkback.c
@@ -80,6 +80,7 @@ __FBSDID("$FreeBSD$");
#include <xen/gnttab.h>
#include <xen/xen_intr.h>
+#include <contrib/xen/arch-x86/cpuid.h>
#include <contrib/xen/event_channel.h>
#include <contrib/xen/grant_table.h>
@@ -101,27 +102,6 @@ __FBSDID("$FreeBSD$");
#define XBB_MAX_REQUESTS \
__CONST_RING_SIZE(blkif, PAGE_SIZE * XBB_MAX_RING_PAGES)
-/**
- * \brief Define to force all I/O to be performed on memory owned by the
- * backend device, with a copy-in/out to the remote domain's memory.
- *
- * \note This option is currently required when this driver's domain is
- * operating in HVM mode on a system using an IOMMU.
- *
- * This driver uses Xen's grant table API to gain access to the memory of
- * the remote domains it serves. When our domain is operating in PV mode,
- * the grant table mechanism directly updates our domain's page table entries
- * to point to the physical pages of the remote domain. This scheme guarantees
- * that blkback and the backing devices it uses can safely perform DMA
- * operations to satisfy requests. In HVM mode, Xen may use a HW IOMMU to
- * insure that our domain cannot DMA to pages owned by another domain. As
- * of Xen 4.0, IOMMU mappings for HVM guests are not updated via the grant
- * table API. For this reason, in HVM mode, we must bounce all requests into
- * memory that is mapped into our domain at domain startup and thus has
- * valid IOMMU mappings.
- */
-#define XBB_USE_BOUNCE_BUFFERS
-
/**
* \brief Define to enable rudimentary request logging to the console.
*/
@@ -257,14 +237,6 @@ struct xbb_xen_reqlist {
*/
uint64_t gnt_base;
-#ifdef XBB_USE_BOUNCE_BUFFERS
- /**
- * Pre-allocated domain local memory used to proxy remote
- * domain memory during I/O operations.
- */
- uint8_t *bounce;
-#endif
-
/**
* Array of grant handles (one per page) used to map this request.
*/
@@ -500,30 +472,6 @@ struct xbb_file_data {
* so we only need one of these.
*/
struct iovec xiovecs[XBB_MAX_SEGMENTS_PER_REQLIST];
-#ifdef XBB_USE_BOUNCE_BUFFERS
-
- /**
- * \brief Array of io vectors used to handle bouncing of file reads.
- *
- * Vnode operations are free to modify uio data during their
- * exectuion. In the case of a read with bounce buffering active,
- * we need some of the data from the original uio in order to
- * bounce-out the read data. This array serves as the temporary
- * storage for this saved data.
- */
- struct iovec saved_xiovecs[XBB_MAX_SEGMENTS_PER_REQLIST];
-
- /**
- * \brief Array of memoized bounce buffer kva offsets used
- * in the file based backend.
- *
- * Due to the way that the mapping of the memory backing an
- * I/O transaction is handled by Xen, a second pass through
- * the request sg elements is unavoidable. We memoize the computed
- * bounce address here to reduce the cost of the second walk.
- */
- void *xiovecs_vaddr[XBB_MAX_SEGMENTS_PER_REQLIST];
-#endif /* XBB_USE_BOUNCE_BUFFERS */
};
/**
@@ -891,25 +839,6 @@ xbb_reqlist_vaddr(struct xbb_xen_reqlist *reqlist, int pagenr, int sector)
return (reqlist->kva + (PAGE_SIZE * pagenr) + (sector << 9));
}
-#ifdef XBB_USE_BOUNCE_BUFFERS
-/**
- * Given a page index and 512b sector offset within that page,
- * calculate an offset into a request's local bounce memory region.
- *
- * \param reqlist The request structure whose bounce region will be accessed.
- * \param pagenr The page index used to compute the bounce offset.
- * \param sector The 512b sector index used to compute the page relative
- * bounce offset.
- *
- * \return The computed global bounce buffer address.
- */
-static inline uint8_t *
-xbb_reqlist_bounce_addr(struct xbb_xen_reqlist *reqlist, int pagenr, int sector)
-{
- return (reqlist->bounce + (PAGE_SIZE * pagenr) + (sector << 9));
-}
-#endif
-
/**
* Given a page number and 512b sector offset within that page,
* calculate an offset into the request's memory region that the
@@ -929,11 +858,7 @@ xbb_reqlist_bounce_addr(struct xbb_xen_reqlist *reqlist, int pagenr, int sector)
static inline uint8_t *
xbb_reqlist_ioaddr(struct xbb_xen_reqlist *reqlist, int pagenr, int sector)
{
-#ifdef XBB_USE_BOUNCE_BUFFERS
- return (xbb_reqlist_bounce_addr(reqlist, pagenr, sector));
-#else
return (xbb_reqlist_vaddr(reqlist, pagenr, sector));
-#endif
}
/**
@@ -1508,17 +1433,6 @@ xbb_bio_done(struct bio *bio)
}
}
-#ifdef XBB_USE_BOUNCE_BUFFERS
- if (bio->bio_cmd == BIO_READ) {
- vm_offset_t kva_offset;
-
- kva_offset = (vm_offset_t)bio->bio_data
- - (vm_offset_t)reqlist->bounce;
- memcpy((uint8_t *)reqlist->kva + kva_offset,
- bio->bio_data, bio->bio_bcount);
- }
-#endif /* XBB_USE_BOUNCE_BUFFERS */
-
/*
* Decrement the pending count for the request list. When we're
* done with the requests, send status back for all of them.
@@ -2180,17 +2094,6 @@ xbb_dispatch_dev(struct xbb_softc *xbb, struct xbb_xen_reqlist *reqlist,
for (bio_idx = 0; bio_idx < nbio; bio_idx++)
{
-#ifdef XBB_USE_BOUNCE_BUFFERS
- vm_offset_t kva_offset;
-
- kva_offset = (vm_offset_t)bios[bio_idx]->bio_data
- - (vm_offset_t)reqlist->bounce;
- if (operation == BIO_WRITE) {
- memcpy(bios[bio_idx]->bio_data,
- (uint8_t *)reqlist->kva + kva_offset,
- bios[bio_idx]->bio_bcount);
- }
-#endif
if (operation == BIO_READ) {
SDT_PROBE3(xbb, kernel, xbb_dispatch_dev, read,
device_get_unit(xbb->dev),
@@ -2241,10 +2144,6 @@ xbb_dispatch_file(struct xbb_softc *xbb, struct xbb_xen_reqlist *reqlist,
struct uio xuio;
struct xbb_sg *xbb_sg;
struct iovec *xiovec;
-#ifdef XBB_USE_BOUNCE_BUFFERS
- void **p_vaddr;
- int saved_uio_iovcnt;
-#endif /* XBB_USE_BOUNCE_BUFFERS */
int error;
file_data = &xbb->backend.file;
@@ -2300,18 +2199,6 @@ xbb_dispatch_file(struct xbb_softc *xbb, struct xbb_xen_reqlist *reqlist,
xiovec = &file_data->xiovecs[xuio.uio_iovcnt];
xiovec->iov_base = xbb_reqlist_ioaddr(reqlist,
seg_idx, xbb_sg->first_sect);
-#ifdef XBB_USE_BOUNCE_BUFFERS
- /*
- * Store the address of the incoming
- * buffer at this particular offset
- * as well, so we can do the copy
- * later without having to do more
- * work to recalculate this address.
- */
- p_vaddr = &file_data->xiovecs_vaddr[xuio.uio_iovcnt];
- *p_vaddr = xbb_reqlist_vaddr(reqlist, seg_idx,
- xbb_sg->first_sect);
-#endif /* XBB_USE_BOUNCE_BUFFERS */
xiovec->iov_len = 0;
xuio.uio_iovcnt++;
}
@@ -2331,28 +2218,6 @@ xbb_dispatch_file(struct xbb_softc *xbb, struct xbb_xen_reqlist *reqlist,
xuio.uio_td = curthread;
-#ifdef XBB_USE_BOUNCE_BUFFERS
- saved_uio_iovcnt = xuio.uio_iovcnt;
-
- if (operation == BIO_WRITE) {
- /* Copy the write data to the local buffer. */
- for (seg_idx = 0, p_vaddr = file_data->xiovecs_vaddr,
- xiovec = xuio.uio_iov; seg_idx < xuio.uio_iovcnt;
- seg_idx++, xiovec++, p_vaddr++) {
- memcpy(xiovec->iov_base, *p_vaddr, xiovec->iov_len);
- }
- } else {
- /*
- * We only need to save off the iovecs in the case of a
- * read, because the copy for the read happens after the
- * VOP_READ(). (The uio will get modified in that call
- * sequence.)
- */
- memcpy(file_data->saved_xiovecs, xuio.uio_iov,
- xuio.uio_iovcnt * sizeof(xuio.uio_iov[0]));
- }
-#endif /* XBB_USE_BOUNCE_BUFFERS */
-
switch (operation) {
case BIO_READ:
@@ -2429,25 +2294,6 @@ xbb_dispatch_file(struct xbb_softc *xbb, struct xbb_xen_reqlist *reqlist,
/* NOTREACHED */
}
-#ifdef XBB_USE_BOUNCE_BUFFERS
- /* We only need to copy here for read operations */
- if (operation == BIO_READ) {
- for (seg_idx = 0, p_vaddr = file_data->xiovecs_vaddr,
- xiovec = file_data->saved_xiovecs;
- seg_idx < saved_uio_iovcnt; seg_idx++,
- xiovec++, p_vaddr++) {
- /*
- * Note that we have to use the copy of the
- * io vector we made above. uiomove() modifies
- * the uio and its referenced vector as uiomove
- * performs the copy, so we can't rely on any
- * state from the original uio.
- */
- memcpy(*p_vaddr, xiovec->iov_base, xiovec->iov_len);
- }
- }
-#endif /* XBB_USE_BOUNCE_BUFFERS */
-
bailout_send_response:
if (error != 0)
@@ -2826,12 +2672,6 @@ xbb_disconnect(struct xbb_softc *xbb)
/* There is one request list for ever allocated request. */
for (i = 0, reqlist = xbb->request_lists;
i < xbb->max_requests; i++, reqlist++){
-#ifdef XBB_USE_BOUNCE_BUFFERS
- if (reqlist->bounce != NULL) {
- free(reqlist->bounce, M_XENBLOCKBACK);
- reqlist->bounce = NULL;
- }
-#endif
if (reqlist->gnt_handles != NULL) {
free(reqlist->gnt_handles, M_XENBLOCKBACK);
reqlist->gnt_handles = NULL;
@@ -3210,17 +3050,6 @@ xbb_alloc_request_lists(struct xbb_softc *xbb)
reqlist->xbb = xbb;
-#ifdef XBB_USE_BOUNCE_BUFFERS
- reqlist->bounce = malloc(xbb->max_reqlist_size,
- M_XENBLOCKBACK, M_NOWAIT);
- if (reqlist->bounce == NULL) {
- xenbus_dev_fatal(xbb->dev, ENOMEM,
- "Unable to allocate request "
- "bounce buffers");
- return (ENOMEM);
- }
-#endif /* XBB_USE_BOUNCE_BUFFERS */
-
reqlist->gnt_handles = malloc(xbb->max_reqlist_segments *
sizeof(*reqlist->gnt_handles),
M_XENBLOCKBACK, M_NOWAIT|M_ZERO);
@@ -3489,14 +3318,29 @@ xbb_attach_failed(struct xbb_softc *xbb, int err, const char *fmt, ...)
static int
xbb_probe(device_t dev)
{
+ uint32_t regs[4];
+
+ if (strcmp(xenbus_get_type(dev), "vbd"))
+ return (ENXIO);
- if (!strcmp(xenbus_get_type(dev), "vbd")) {
- device_set_desc(dev, "Backend Virtual Block Device");
- device_quiet(dev);
- return (0);
- }
+ KASSERT(xen_cpuid_base != 0, ("Invalid base Xen CPUID leaf"));
+ cpuid_count(xen_cpuid_base + 4, 0, regs);
- return (ENXIO);
+ /* Only attach if Xen creates IOMMU entries for grant mapped pages. */
+ if (!(regs[0] & XEN_HVM_CPUID_IOMMU_MAPPINGS)) {
+ static bool warned;
+
+ if (!warned) {
+ warned = true;
+ printf(
+ "xen-blkback disabled due to grant maps lacking IOMMU entries\n");
+ }
+ return (ENXIO);
+ }
+
+ device_set_desc(dev, "Backend Virtual Block Device");
+ device_quiet(dev);
+ return (0);
}
/**