With acce728cbc6c we disallowed configuring 64-bit guests on
32-bit hosts, but forgot to document that in removed-features.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 docs/about/removed-features.rst | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/docs/about/removed-features.rst b/docs/about/removed-features.rst
index 2527a91795..790a5e481c 100644
--- a/docs/about/removed-features.rst
+++ b/docs/about/removed-features.rst
@@ -858,6 +858,15 @@ QEMU.  Since all recent x86 hardware from the past >10 years is
 capable of the 64-bit x86 extensions, a corresponding 64-bit OS should
 be used instead.
 
+32-bit hosts for 64-bit guests (removed in 10.0)
+''''''''''''''''''''''''''''''''''''''''''''''''
+
+In general, 32-bit hosts cannot support the memory space or atomicity
+requirements of 64-bit guests.  Prior to 10.0, QEMU attempted to
+work around the atomicity issues in system mode by running all vCPUs
+in a single thread context; in user mode atomicity was simply broken.
+From 10.0, QEMU has disabled configuration of 64-bit guests on 32-bit hosts.
+
 Guest Emulator ISAs
 -------------------
 
-- 
2.43.0

On Sat, Apr 12, 2025 at 12:43 PM Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> With acce728cbc6c we disallowed configuring 64-bit guests on
> 32-bit hosts, but forgot to document that in removed-features.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  docs/about/removed-features.rst | 9 +++++++++
>  1 file changed, 9 insertions(+)

Merged for 10.0 via Michael Tokarev's trivial patches pull request.

Stefan

>
> diff --git a/docs/about/removed-features.rst b/docs/about/removed-features.rst
> index 2527a91795..790a5e481c 100644
> --- a/docs/about/removed-features.rst
> +++ b/docs/about/removed-features.rst
> @@ -858,6 +858,15 @@ QEMU.  Since all recent x86 hardware from the past >10 years is
>  capable of the 64-bit x86 extensions, a corresponding 64-bit OS should
>  be used instead.
>
> +32-bit hosts for 64-bit guests (removed in 10.0)
> +''''''''''''''''''''''''''''''''''''''''''''''''
> +
> +In general, 32-bit hosts cannot support the memory space or atomicity
> +requirements of 64-bit guests.  Prior to 10.0, QEMU attempted to
> +work around the atomicity issues in system mode by running all vCPUs
> +in a single thread context; in user mode atomicity was simply broken.
> +From 10.0, QEMU has disabled configuration of 64-bit guests on 32-bit hosts.
> +
>  Guest Emulator ISAs
>  -------------------
>
> --
> 2.43.0
>

On 4/14/25 08:16, Stefan Hajnoczi wrote:
> On Sat, Apr 12, 2025 at 12:43 PM Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> With acce728cbc6c we disallowed configuring 64-bit guests on
>> 32-bit hosts, but forgot to document that in removed-features.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>   docs/about/removed-features.rst | 9 +++++++++
>>   1 file changed, 9 insertions(+)
> 
> Merged for 10.0 via Michael Tokarev's trivial patches pull request.

Thanks, guys.


r~

On 12/4/25 18:43, Richard Henderson wrote:
> With acce728cbc6c we disallowed configuring 64-bit guests on
> 32-bit hosts, but forgot to document that in removed-features.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   docs/about/removed-features.rst | 9 +++++++++
>   1 file changed, 9 insertions(+)
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Richard Henderson <richard.henderson@linaro.org> writes:

> With acce728cbc6c we disallowed configuring 64-bit guests on
> 32-bit hosts, but forgot to document that in removed-features.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro

On Sat, Apr 12, 2025 at 09:43:15AM -0700, Richard Henderson wrote:
> With acce728cbc6c we disallowed configuring 64-bit guests on
> 32-bit hosts, but forgot to document that in removed-features.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  docs/about/removed-features.rst | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/docs/about/removed-features.rst b/docs/about/removed-features.rst
> index 2527a91795..790a5e481c 100644
> --- a/docs/about/removed-features.rst
> +++ b/docs/about/removed-features.rst
> @@ -858,6 +858,15 @@ QEMU.  Since all recent x86 hardware from the past >10 years is
>  capable of the 64-bit x86 extensions, a corresponding 64-bit OS should
>  be used instead.
>  
> +32-bit hosts for 64-bit guests (removed in 10.0)
> +''''''''''''''''''''''''''''''''''''''''''''''''
> +
> +In general, 32-bit hosts cannot support the memory space or atomicity
> +requirements of 64-bit guests.  Prior to 10.0, QEMU attempted to
> +work around the atomicity issues in system mode by running all vCPUs
> +in a single thread context; in user mode atomicity was simply broken.
> +From 10.0, QEMU has disabled configuration of 64-bit guests on 32-bit hosts.
> +
>  Guest Emulator ISAs
>  -------------------

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

With regards,
Daniel
-- 
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