Re: [PATCH v2] mshv: Fix deposit memory in MSHV_ROOT_HVCALL

[Wei Liu <wei.liu@kernel.org>]

On Fri, Oct 17, 2025 at 11:58:17AM -0700, Nuno Das Neves wrote:
> When the MSHV_ROOT_HVCALL ioctl is executing a hypercall, and gets
> HV_STATUS_INSUFFICIENT_MEMORY, it deposits memory and then returns
> -EAGAIN to userspace. The expectation is that the VMM will retry.
> 
> However, some VMM code in the wild doesn't do this and simply fails.
> Rather than force the VMM to retry, change the ioctl to deposit
> memory on demand and immediately retry the hypercall as is done with
> all the other hypercall helper functions.
> 
> In addition to making the ioctl easier to use, removing the need for
> multiple syscalls improves performance.
> 
> There is a complication: unlike the other hypercall helper functions,
> in MSHV_ROOT_HVCALL the input is opaque to the kernel. This is
> problematic for rep hypercalls, because the next part of the input
> list can't be copied on each loop after depositing pages (this was
> the original reason for returning -EAGAIN in this case).
> 
> Introduce hv_do_rep_hypercall_ex(), which adds a 'rep_start'
> parameter. This solves the issue, allowing the deposit loop in
> MSHV_ROOT_HVCALL to restart a rep hypercall after depositing pages
> partway through.
> 
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>

In v1 you said you will add a "Fixes" tag. Where is it?

Wei