Re: [PATCH 0/5] Fix register page use for guests using mshv accel

[Magnus Kulke <magnuskulke@linux.microsoft.com>]

On Wed, Jul 08, 2026 at 01:16:40AM +0300, Doru Blânzeanu wrote:
> This patch series is a fix for the recent merge of the outdated patch series:
> https://lore.kernel.org/all/20260428135053.251200-1-dblanzeanu@linux.microsoft.com/
> 
> The above patch series had some newer versions that fixed addressed feedback
> from reviewers.
> 
> The commits do the following:
> 1. Moves the definition for the `hv_vp_register_page` to `hvhdk.h`
>    Fixes: 8afb40b7fe
> 2. Changes the register page setup to fail in case the mmap of the page fails.
>    This way it signals an issue early.
>    Fixes: a173f8f170
> 3. Rename functions local to the `mshv-cpu.c` linked to register page get.
>    Use the register page to read registers on VM exit. General purpose
>    registers, RIP, RFLAGS, segment registers, and control registers
>    (CR0, CR4, CR4, CR8, EFER) are read directly from the page. Registers
>    not present on the page (TR, LDTR, GDTR, IDTR, CR2, APIC_BASE) are not
>    fetched anymore for performance reasons.
>    Removes the fallback to ioctls in case the register page is not correctly set
>    up and aborts.
>    Fixes: 40072a7391
> 4. Changes the registers storing to only use the register page and not rely on
>    ioctls for perfomance improvements. From local tests, the special registers
>    that are not stored, do not get modified when emulating. However, if there's
>    an issue discovered, we'll fix later.
>    Fixes: 80c7f8e9cd
> 5. When a device handler (e.g. vmport) calls cpu_synchronize_state() during
>    I/O port dispatch, it sets cpu->accel->dirty = true and may modify
>    registers directly in env. The old PIO code ignored this: it
>    unconditionally wrote the stale info->rax from the VM-exit intercept
>    message back to the hypervisor and then cleared dirty, discarding any
>    register changes made by the device.
>    Note: This was a change present in version 3 of the patch series but not
>    present in the version 1 of the patch series (the one merged)
> 
> The register page is only used when it has been successfully mmapped and
> the hypervisor has marked it as valid (`isvalid != 0`). Otherwise, an error is
> returned and execution aborted to signal something faulty and unexpected.
> 
> Changes since v1:
> - Rebased on latest master to fix a merge conflict coming from the elimination
>   of the accel specific dirty field
> 
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> 
> Doru Blânzeanu (5):
>   include/hw/hyperv: move hv_vp_register_page struct definition
>   target/i386/mshv: abort when hv_vp_register_page setup fails
>   target/i386/mshv: remove fallback for register page get registers
>   target/i386/mshv: remove fallback for register page set registers
>   target/i386/mshv: fix pio handlers clobbering device-modified
>     registers
> 
>  include/hw/hyperv/hvgdk.h      |   2 +
>  include/hw/hyperv/hvgdk_mini.h | 103 --------------
>  include/hw/hyperv/hvhdk.h      | 106 ++++++++++++++
>  target/i386/mshv/mshv-cpu.c    | 247 +++++++++++++++------------------
>  4 files changed, 219 insertions(+), 239 deletions(-)
> 
> -- 
> 2.53.0

included in mkulke-pull-20261006