This reverts commit aad7b5c11d51d57659978e04702ac970906894e8.
The change from OvmfX64 to OvmfXen causes a change in behaviour, whereby
OvmfXen maps its shared info page at the top of address space. When trying to
migrate such a domain, XENMEM_maximum_gpfn returns a very large value. This
has uncovered multiple issues:
1) The userspace hypercall wrappers truncate all return values to int on
Linux and Solaris. This needs fixing in Xen.
2) 32bit toolstacks can't migrate any domain with RAM above the 2^40 mark,
because of virtual address constraints. This needs fixing in OVMF.
Fixes for both of these aren't completely trivial. Revert the change to
unblock staging in the meantime.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Anthony PERARD <anthony.perard@citrix.com>
CC: George Dunlap <George.Dunlap@eu.citrix.com>
CC: Ian Jackson <iwj@xenproject.org>
CC: Jan Beulich <JBeulich@suse.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Wei Liu <wl@xen.org>
CC: Julien Grall <julien@xen.org>
---
tools/firmware/ovmf-makefile | 10 ++--------
1 file changed, 2 insertions(+), 8 deletions(-)
diff --git a/tools/firmware/ovmf-makefile b/tools/firmware/ovmf-makefile
index 637ee509c3..55f9992145 100644
--- a/tools/firmware/ovmf-makefile
+++ b/tools/firmware/ovmf-makefile
@@ -17,14 +17,8 @@ all: build
.PHONY: build
build:
if test -e .git ; then $(GIT) submodule update --init --recursive ; fi
- set -ex; \
- if test -e OvmfPkg/OvmfXen.dsc; then \
- OvmfPkg/build.sh -a X64 -b $(TARGET) -n 4 -p OvmfPkg/OvmfXen.dsc; \
- cp Build/OvmfXen/$(TARGET)_GCC*/FV/OVMF.fd ovmf.bin; \
- else \
- OvmfPkg/build.sh -a X64 -b $(TARGET) -n 4; \
- cp Build/OvmfX64/$(TARGET)_GCC*/FV/OVMF.fd ovmf.bin; \
- fi
+ OvmfPkg/build.sh -a X64 -b $(TARGET) -n 4
+ cp Build/OvmfX64/$(TARGET)_GCC*/FV/OVMF.fd ovmf.bin
.PHONY: clean
clean:
--
2.11.0
On Tue, Jun 22, 2021 at 04:39:30PM +0100, Andrew Cooper wrote: > This reverts commit aad7b5c11d51d57659978e04702ac970906894e8. > > The change from OvmfX64 to OvmfXen causes a change in behaviour, whereby > OvmfXen maps its shared info page at the top of address space. When trying to > migrate such a domain, XENMEM_maximum_gpfn returns a very large value. This > has uncovered multiple issues: > > 1) The userspace hypercall wrappers truncate all return values to int on > Linux and Solaris. This needs fixing in Xen. > 2) 32bit toolstacks can't migrate any domain with RAM above the 2^40 mark, > because of virtual address constraints. This needs fixing in OVMF. > > Fixes for both of these aren't completely trivial. Revert the change to > unblock staging in the meantime. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Anthony PERARD <anthony.perard@citrix.com> Thanks, -- Anthony PERARD
On 22.06.2021 17:39, Andrew Cooper wrote: > This reverts commit aad7b5c11d51d57659978e04702ac970906894e8. > > The change from OvmfX64 to OvmfXen causes a change in behaviour, whereby > OvmfXen maps its shared info page at the top of address space. When trying to > migrate such a domain, XENMEM_maximum_gpfn returns a very large value. This > has uncovered multiple issues: > > 1) The userspace hypercall wrappers truncate all return values to int on > Linux and Solaris. This needs fixing in Xen. > 2) 32bit toolstacks can't migrate any domain with RAM above the 2^40 mark, > because of virtual address constraints. This needs fixing in OVMF. And I suspect even that presently enforce boundary of 2^40 is actually too high, and things still wouldn't work when getting close. At the very least the tool stack then depends on a fairly big chunk of memory (2^30 bytes) to be available in one single, virtually contiguous piece. Iirc 32-bit Linux can be configured to not even leave this much space for user mode. Jan
On 22/06/2021 17:10, Jan Beulich wrote: > On 22.06.2021 17:39, Andrew Cooper wrote: >> This reverts commit aad7b5c11d51d57659978e04702ac970906894e8. >> >> The change from OvmfX64 to OvmfXen causes a change in behaviour, whereby >> OvmfXen maps its shared info page at the top of address space. When trying to >> migrate such a domain, XENMEM_maximum_gpfn returns a very large value. This >> has uncovered multiple issues: >> >> 1) The userspace hypercall wrappers truncate all return values to int on >> Linux and Solaris. This needs fixing in Xen. >> 2) 32bit toolstacks can't migrate any domain with RAM above the 2^40 mark, >> because of virtual address constraints. This needs fixing in OVMF. > And I suspect even that presently enforce boundary of 2^40 is actually > too high, and things still wouldn't work when getting close. At the > very least the tool stack then depends on a fairly big chunk of memory > (2^30 bytes) to be available in one single, virtually contiguous piece. > Iirc 32-bit Linux can be configured to not even leave this much space > for user mode. I tested it once during Migration v2 development, and it worked for me, but I do expect that that is as much testing as it has had since... A 3G/1G split is the default under multiple 32bit kernels, and the allocation is made right at the start, so there is a reasonable chance of finding space. After all, it only needs 4k alignment. Whether ASLR has changed the chances in the meantime remains to be seen, but honestly - 32bit toolstacks on x86 really don't exist in production any more, and Arm still hasn't implemented logdirty support, so the limit has little practical consequence. ~Andrew
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