6.6-stable review patch. If anyone has any objections, please let me know.
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From: Stanislav Spassov stanspas@amazon.de
[ Upstream commit 1937e18cc3cf27e2b3ef70e8c161437051ab7608 ]
Ongoing work on an optimization to batch-preallocate vCPU state buffers for KVM revealed a mismatch between the allocation sizes used in fpu_alloc_guest_fpstate() and fpstate_realloc(). While the former allocates a buffer sized to fit the default set of XSAVE features in UABI form (as per fpu_user_cfg), the latter uses its ksize argument derived (for the requested set of features) in the same way as the sizes found in fpu_kernel_cfg, i.e. using the compacted in-kernel representation.
The correct size to use for guest FPU state should indeed be the kernel one as seen in fpstate_realloc(). The original issue likely went unnoticed through a combination of UABI size typically being larger than or equal to kernel size, and/or both amounting to the same number of allocated 4K pages.
Fixes: 69f6ed1d14c6 ("x86/fpu: Provide infrastructure for KVM FPU cleanup") Signed-off-by: Stanislav Spassov stanspas@amazon.de Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lore.kernel.org/r/20250218141045.85201-1-stanspas@amazon.de Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/fpu/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 4b414b0ab0692..db200990b5569 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -220,7 +220,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu) struct fpstate *fpstate; unsigned int size;
- size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64); + size = fpu_kernel_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64); fpstate = vzalloc(size); if (!fpstate) return false;